Part 617 - SOIL SURVEY INTERPRETATIONS
CONTENTS
PART
TITLE
PAGE
617.00
Definition and Purpose ......................................................................................................... 617-1
617.01
Policy and Responsibilities................................................................................................... 617-1
617.02
General.................................................................................................................................. 617-2
617.03
Interpretations for Map Unit Components and Map Units ................................................... 617-2
617.04
Developing and Maintaining Interpretation Guides and Ratings ......................................... 617-3
617.05
Reviewing and Implementing Soil Interpretative Technologies .......................................... 617-3
617.06
The National Soil Information System ................................................................................ 617-3
617.07
Presenting Soil Interpretations ............................................................................................. 617-4
617.08
Updating Soil Interpretations................................................................................................ 617-4
617.09
Coordinating Soil Survey Interpretations ............................................................................. 617-4
617.10
Writing Soil Interpretation Criteria ...................................................................................... 617-4
(430-VI-NSSH, 1999)
i
Part 617 - SOIL SURVEY INTERPRETATIONS
617.00 Definition and Purpose.
617.01 Policy and Responsibilities.
(a) Soil survey interpretations predict soil
behavior for specified soil uses and under
specified soil management practices. They help to
implement laws, programs, and regulations at
local, State, and National levels. They assist the
planning of broad categories of land use, such as
cropland, rangeland, pastureland, forestland, or
urban development. Soil survey interpretations
also help to plan specific management practices
that are applied to soils, such as irrigation of
cropland or equipment use.
(a) The criteria used to develop a soil
interpretation is retained by the office providing
the interpretation.
(b) Soil interpretations provide users of soil
survey information with predictions of soil
behavior to help in the development of reasonable
and effective alternatives for the use and
management of soil, water, air, plant, and animal
resources.
(c) Prediction of soil behavior results from the
observation and record of soil responses to
specific uses and management practices, such as
seasonal wet soil moisture status and the resultant
effect in a basement. Recorded observations
validate predictive models. The models project
the expected behavior of similar soils from the
behavior of observed soils.
(d) Soil interpretations use soil properties or
qualities that directly influence a specified use or
management of the soil. Soil properties and
qualities that characterize the soil are criteria for
interpretation models. These properties and
qualities include (1) site features, such as slope
gradient; (2) individual horizon features, such as
particle size; and (3) characteristics that pertain to
soil as a whole, such as depth to a restrictive layer.
(e) Laboratory and field measurements, models
and inferences from soil properties, morphology,
and geomorphic characteristics provide the values
used for estimating soil properties. Sources of
laboratory data commonly are the Soil Survey
Laboratory, Agricultural Experiment Station
laboratories, and State Highway Department
testing laboratories. Pedon descriptions record
field measurements, field observations, and
descriptions of soil morphology.
(b) Only the National Soil Survey Center
approves deviations from the standard procedures
for populating data elements in part 618 .
Deviations from the nationally supported
interpretation criteria referenced in parts 620 and
622 are documented and renamed by the state.
National program applications use the standard
set.
(c) Interpretation development follows the
procedure in part 617.10.
(d) The Memorandum of Understanding states
which interpretations will be made for a soil
survey area. The MLRA office, state soil
scientist, and cooperators agree on whether or not
to generate interpretations for miscellaneous land
types and minor soil components. The Soil
Survey Division encourages the entry of data and
preparation of soil interpretations for
miscellaneous areas. Omission of data elements is
by joint consensus of the MLRA office, state soil
scientist, and cooperators.
(e) Completely populate the data elements that
are used as criteria in an interpretation in order to
generate reliable interpretations.
(f) Completely populate the data elements for
major soil components including map unit
components classified as higher taxonomic
categories. The MLRA office, state soil scientist,
and cooperators should reach a joint decision for
special situations where it is not practical to
populate data elements for map unit components
classified at a higher taxonomic category than soil
series. If the range of properties is too wide for
interpretations, these areas may not meet the
requirements of the user defined needs of the
survey.
(g) The MLRA office is responsible for:
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617-2 Part 617 - Soil Interpretations
-- the quality assurance, development,
maintenance, and coordination of soil
interpretative data and information for the
private and State land.
-- assuring that interpretations are made
according to current policy and guidelines;
-- reviewing all interpretations to assure
technical accuracy and the consistency of the
soil data and interpretations
-- assuring that soil performance is correlated to
soils according to current policy and
guidelines; and
-- keeping all soil data element information
current and complete in the national soil
information system database.
(h) The state soil scientist is responsible for:
-- assisting soil survey users in understanding
and applying soil survey information;
-- coordinating the development of localized
soil interpretations;
-- ensuring the technical content, coordination,
and quality of soil information in the field
office technical guides);
-- providing soils input to all NRCS program
activities; and
-- supplementing the state subset of the national
soil information system data with
state/county specific interpretation items.
(i) The appropriate representative of Federal
agencies is responsible for the soil interpretations
for Federally administered lands.
(j) The National Soil Survey Center is
responsible for:
-- providing training in developing,
maintaining, storing, and retrieving soil
interpretations;
-- developing policy, standards, guidelines, and
procedures for making soil interpretations;
--coordinating with other disciplines and
program managers in the development of soil
interpretations with national application; and
-- sharing and providing guidance on soil
interpretations that are used in soil survey
publications, reports, and databases.
617.02 General.
(a) Standard soil survey interpretations are
nationwide in scope and application. These
interpretations and their related criteria are for
national application. The National Soil Survey
Center and specific disciplines at the National
level maintain the criteria.
Regional, state, or local soil survey
interpretations and their related guides support
interpretations in a specific area. They use
regional, state, or local criteria. MLRA regional
or State offices maintain the criteria.
(b) The cooperators in the National Cooperative
Soil Survey (NCSS) develop soil interpretations
that support user needs. The Natural Resources
Conservation Service (NRCS) maintains them.
Published soil surveys and advance soil surveys
include soil interpretations. Thematic maps using
geographical information systems (GIS) provide
an alternate interpretation format.
(c) An individual soil survey area may have a
wide range of land uses for which soil
interpretations are developed, maintained, and
published. Local, state, and MLRA offices and
NCSS participants select the land uses and
primary interpretations to be published. The soil
survey memorandum of understanding documents
these selections.
(d) States, MLRA offices, and cooperators
develop additional interpretations after publication
for users requesting assistance.
617.03 Interpretations for Map Unit
Components and Map Units.
(a) Soil interpretations support (1) detailed soil
survey maps, such as from the Soil Survey
Geographic (SSURGO) database, (2) general soil
maps, such as from the State Soil Geographic
(STATSGO) database, and (3) the more general
soil maps, such as from the national major land
resource area map
Soil survey interpretations primarily address
soil map unit components. Most map unit
components have a complete set of data elements
sufficient for making interpretations, but some
components lack needed data. The completeness
and accuracy of data elements that are used as soil
interpretation criteria determines the accuracy of
interpretations. Review the completeness of the
database prior to release of interpretations to
users. The reports from the NASIS interpretation
generator show where data is missing.
When miscellaneous areas are components in
map units, list them in interpretative tables.
(430-VI-NSSH, 1999)
Part 617 - Soil Interpretations 617-3
Determine suitabilities and limitations by onsite
investigation.
Occasionally interpretative ratings represent the
map unit as a whole. Performance statements
which apply to soil map unit(s) as a whole use two
methods for presentation:
(1) as percentages of the unit with a specific
rating, such as "map unit Alpha-Beta
complex, 0 to 3 percent slopes is 60 percent
well suited and 40 percent poorly suited for
the specified use" or
(2) (2) as a single rating that was averaged
from values or determined from preset
percentages, for example a single yield of
crops is given, which is calculated from the
percent composition of the map unit.
Map unit interpretations generally address
queries from users. They may need information
on the major components of a map unit or may
need information on the minor components if the
minor components are important to a specific use.
(b) Interpretations for the map units displayed
on the State Soil Geographic (STATSGO)
database, the major land resource database, and
other general soil maps generalize interpretations
more than the interpretations for the map units
displayed on the Soil Survey Geographic
(SSURGO) database and other detailed soil survey
maps. They are more general because general soil
map units commonly contain more map unit
components or more broadly defined data than the
map units of the more detailed soil survey maps.
Performance statements for general soil map units
apply to the map unit as a whole and express the
percentage of the map unit that meets the
performance criteria. For example "the AlphaBeta-Gamma map unit is 60 percent well suited,
25 percent poorly suited, and 15 percent unsuited
for the specified use."
617.04 Developing and Maintaining
Interpretation Guides and Ratings.
Standard interpretation data and information
rely on guides for interpreting soils as referenced
in part 620 and in part 622, or as approved
separately by the National Soil Survey Center and
other national disciplines.
The National Soil Survey Center leads the
development, maintenance, and updating of soil
interpretive technology and develops policy
relating to the application of soil data and national
interpretations. Discipline specialists, such as
agronomists, foresters, and range conservationists,
are essential to the development of soil
interpretation guides and standards and in the
technical transfer of the resultant interpretations
and information to users.
The State, regional, or National offices develop
soil interpretations and related guides .
Interdisciplinary teams develop soil interpretations
and related guides for specific soil interpretations.
Specialists concerned with a given land use or
resource work together in developing the initial
criteria, field-testing the criteria, and developing
the final guide for interpreting soils for a specified
use. The procedure outlined in part 617.10
governs the development and documentation of
the proposal.
617.05 Reviewing and Implementing
Soil Interpretative Technologies.
A project soil survey staff, state office staff, or
NCSS participant propose and develope soil
interpretative guides and criteria. These offices
submit the proposed changes to standard
interpretative guides and criteria to the National
Soil Survey Center. Submission of regional, state,
or local interpretations to the National Soil Survey
Center enable the center to share these
developments with potential users. Soil
interpretations meet the requirements outlined in
part 617.10. Field observations, research
(laboratory and/or field), and other documentation
support them.
617.06 The National Soil
Information System.
The National soil information system records
soil survey data, soil performance, and
interpretations. Soil interpretations attach to map
unit components. Part 618 of this handbook
discusses specific data entry.
The soil interpretations information that are
prepared for soil components contain all necessary
criteria for computer generated interpretations.
The consistency of the entry of specific soil
properties leads to the coordination of soil
interpretations for map units with other MLRA
(430-VI-NSSH, 1999)
617-4 Part 617 - Soil Interpretations
office areas and regions. All interpretations match
exactly when areas share the same data mapunit.
617.07 Presenting Soil
Interpretations.
The method by which soil interpretations are
presented, such as in tables, databases,
interpretative sheets, and special reports provides
easily understood soil limitations, suitabilities, or
potentials for a specific use. Thematic maps
effectively present soil limitations and potentials.
A series of thematic maps, each focusing on a
single soil attribute or interpretation, help many
users. For more general use, tables or narrative
forms of soil interpretations and potentials are the
more common technique.
617.08 Updating Soil
Interpretations.
(a) The evaluation and updating of soil
interpretations is a dynamic process. Changes in
soil use or land management practices require
new, revised, or updated interpretations. These
changes initiate the revision and updating of soil
interpretations. Update soil interpretations
periodically as more information is learned about
a soil and its behavior or as soil properties change
due to activities by man or nature.
(b) Although the soil maps contained in
published soil surveys generally remain valid for
many years, the information about the soils that
are delineated on the maps is continually updated
and enhanced as research is conducted or as new
kinds of data are collected.
(c) New uses for a soil or new practices that
have no existing soil interpretations may become
important in an area and thus require the
development of new interpretations or the
modification of an existing interpretation for a
similar use or practice.
617.09 Coordinating Soil Survey
Interpretations.
(a) For the major land resource area, specific
interpretations for similar phases of a named kind
of soil are identical except for minor differences
that can be justified by local variations, such as in
climate or topography. Similar soils have similar
interpretations. Interpretations in field office
technical guides and soil handbooks should be
consistent with the coordinated soil survey
interpretations for the major land resource area.
(b) MLRA office soil scientists are responsible
for coordinating soil survey interpretations and
significant revisions to those map unit components
in their region. Responsibility also consists of
coordinating with the adjoining regions, reviewing
measured and observed data from all areas in
which similar map units occur. and developing
ratings and predictions of behavior based on these
data. State and program specific interpretive
groups are the responsibility of the state soil
scientist.
(c) Nonstandard guides to populate data
elements or incomplete and uncoordinated entries
for map unit components cause coordination
problems.
617.10 Writing Soil Interpretation
Criteria.
In developing interpretations criteria, involve
the user. Also consider the clarity, accuracy, and
the ability of the criteria to be easily created and
modified. Local, State, regional, and National
offices develop criteria to represent user needs.
They follow a consistent procedure and firmly
establish principles for documentation. Consider
the ease of development and the stability of the
interpretation. Use the expert judgment of
specialists. People who work with the intended
use and application know more than what can be
speculated by those people with less experience.
The following steps lead to the goals for
interpretation criteria.
Step 1. Define the Activity.
Clearly and very specifically define the activity
or use to be interpreted. When defining the
activity:
-- describe the activity or use;
-- identify the purpose or purposes of the
activity or use;
-- define the desired performance of the activity
or use;
-- specify the soil depths that are affected;
-- identify the type of equipment for
installation;
(430-VI-NSSH, 1999)
Part 617 - Soil Interpretations 617-5
-- mention resource conditions that indicate a
different activity or use or the misuse of this
practice;
-- define the needed specific geographic detail,
including the length and width and the
direction of application if important; and
-- define the needed map and interpretation
reliability and uniformity.
Cite references that help to define the activity.
Literature citations, such as information from the
State Health Department, bulletins, or soil
performance research, support the decision made
and help track the procedure.
Step 2. Separate Aspects.
Separate different aspects of the activity for
separate interpretations. Aspects of
interpretations are planning elements that require
different criteria, such as installation,
performance, maintenance, and effect. Proceed
through the steps to develop criteria for each
aspect. Each aspect is a unique interpretation that
has separate criteria and users. Mention other
aspects that may need interpretation but are not
addressed.
Step 3. Identify Site Features.
Identify significant site features significant for
the interpretation and any assumptions about
them. Site features are not soil properties, but are
features such as climate factors, landscape
stability hazard, vegetation, and surface
characteristics. Identify and record the implied
affect of site features on each aspect of the
interpretation. Although site features are not soil
properties, they are commonly recorded on soil
databases and are valuable for developing
interpretations because they are geographically
specific to soils.
Step 4. List Soil Properties.
Identify and list the specific soil properties that
are significant to the interpretation. Use only
basic properties, qualities, or observed properties
and do not make interpretations from previous
interpretations or models. Generally, terms that
refer to classes fit in this category. Only use
derived soil qualities when they are derived within
the criteria to ensure the integrity of the data and
the resultant interpretation. Terms used as
properties or qualities that have inconsistent
entries or derivation pathways result in
inconsistent interpretations. Concentrating on the
basic influencing property that has the most
consistent database entries provides for more
consistent interpretations. For example, consider
the soil moisture status during a construction
period and not the drainage class. Minimize the
list of properties by identifying only the basic
properties. Review the list to ensure that the same
property is not implied several times. For
example, USDA texture, clay, and AASHTO do
not need to appear on the same list.
Step 5. Select the Number of Separations.
Select the number of interpretative separations,
and define the intent of the separation or
classification. Each separation should have a
purpose, which normally represents a significant
management grouping and a need for separate
treatment. Commonly used terms in separations
are slight, moderate, and severe or good, fair, and
poor. User needs dictate the number of
separations. The levels of user needs may vary.
Some users do not use groupings.
Step 6. Document Assumptions.
Document assumptions about the significance
of the property and established values for
separating criteria.
(a) A record of the significance of the property
helps to define the property and allows for future
understanding and modification. It provides a
basis for the criteria so that changes can be made
if different equipment is used.
(b) Indicate why the feature is important and
why the specific break was chosen, such as why 6
percent slope was used instead of 10 percent
slope. If the limit is arbitrary or speculated, state
that it is but also indicate the intent of the
separation. The new interpretation generator
recognizes the progressive effect of a property on
the interpretation. The curve for approximate
reasoning (fuzzy logic) reflects the increasing,
decreasing, or constant effect that varying degrees
of a property have on the interpretation. The
evaluation phase of the interpretation generator
uses the curve.
(c) Establish values that are significant to the
interpretation and not to the mapping. The values
should represent the significance to an activity.
Do not consider how soils were grouped in
mapping since these groupings may have been
made for other interpretations.
Step 7. Develop the Criteria Table.
Assign feature and impact terms, and develop
the criteria table. The following categories of
column headings are recommended for use in the
criteria table:
(430-VI-NSSH, 1999)
617-6 Part 617 - Soil Interpretations
-- Factor (this is the soil property);
-- Degree of Limitation (such as Slight,
Moderate, Severe);
-- Feature (the term to be displayed for soil
property); and
-- Impact (the dominant impact that the soil
property has on the practice being rated).
Information in the feature and impact columns is
helpful in designing ways to overcome the
limitation. Ensure that all terms are added to data
dictionary.
Step 8. Application, Presentation, and Testing.
(a) Database needs.
Provide a description of the calculation
procedure. The calculation procedure is a set of
instructions for the correct access to dataset
entries. It is needed to sort criteria from a
database without questioning the intention of the
interpretation. The description should be specific
to the database being used. Instructions for using
high, low, or central values of data should be
given in this description.
(b) Temporal considerations for application.
The time dependent or temporal properties or
events from the measured permanent features of
the soil.
(1) Flooding and periods of freezing,
wetness, or dryness are significant at the time they
occur but not at all times. For example, in
planning an installation phase, remember that this
phase can be scheduled for alternate times when
these events are not significant to the criteria. In
these situations, temporal properties should not be
part of the criteria unless a practice is being rated
for a particular time of the year.
(2) If temporal events are important for the
permanent performance of the interpretation, then
include them in the rating criteria.
(3) State the soil moisture condition or the
time of the year to which the interpretation
applies. Since the conditions of soil moisture and
soil freezing vary throughout the year and these
conditions affect soil properties, criteria should
define stated moisture conditions. Criteria can be
developed for different times of the year by
defining the criteria for the conditions that exist at
the desired time of the year. Information on soil
moisture status and freezing conditions are in the
National Soil Information System.
(c) Reliability.
(1) Each soil property has a reliability
connected to it. Soil property entries may come
from measurements, derivations, or estimates.
Consider the soil property reliability to inform the
users of the reliability of the expected
interpretation.
(2) Properties vary according to time of the
year. If so specify a time of the year for the
interpretation. The reliability of the interpretation
often depends on the seasonal variation of the
property. Information presented to the user on
temporal variation helps to describe the reliability
of the interpretation.
(3) Geographic reliability refers to the areal
extent to which an interpretation can be applied.
Statements about the consistency, variability, or
uniformity of a soil delineation help to define the
geographic reliability of the interpretation.
(d) Testing.
Interpretations should be tested against the
actual effects on activities or practice
performance. Many properties and criteria need
further refinement before they can be used. Some
terms, such as flooding, require clarifying
statements such as for velocity, depth, or duration.
Sources of information other than the soil
interpretations record(s) may be available and
should be considered at this stage of criteria
development. Also consider related refinements
and onsite investigations.
(1) Keep in mind that a soil interpretation is
for planning purposes. Additional refinements or
other resource information can be used for site
selection. Soil interpretations alone may not
answer all the questions. Inform the intended user
about other information that may be needed.
Honestly express the limitations of the
interpretation but do not undersell the information.
Many users have no other resource information.
(2) For the final selection of a site, an onsite
investigation may be needed to provide
information more specific than that in a standard
soil survey. Onsite investigation is recommended
for expensive installations and for the
determination of design criteria.
(3) Use benchmarks for testing
interpretations. A benchmark soil and site
description and the desired interpretation rating
may help to stabilize the criteria. As criteria is
developed and adjusted, test the criteria against
the benchmark set of properties.
(430-VI-NSSH, 1999)
Part 617 - Soil Interpretations 617-7
(e) Date the interpretation and criteria.
To verify the criteria used, it is important to
date the criteria and the interpretation tables. As
criteria is modified, it may not be apparent that the
tables were not also made from current criteria.
(430-VI-NSSH, 1999)