Soil Survey: The Foundation for Productive Natural Resource
Management
Extension Bulletin 60, April
1993
Bruce Seelig, Water Quality Specialist
What is a soil? How does one soil differ from another?
How can we use our soils to provide food and fiber for present needs and still maintain
them for future generations? Soil maps and the information that accompanies them—soil
survey reports—provide answers to these questions and many others.
What is a soil survey
How soil surveys are made
Information contained in soil survey reports
Finding information about the soils on your farm or ranch
How a soil survey report can be of use to you
New uses and applications of soil survey information
Do soil maps have limitations?
Soil surveys can help you manage your resources for sustained productivity
Where to obtain soil survey information
What is a soil survey
A soil survey is an inventory of the soil resources of a county
or area. It consists of a soil map, descriptions of the soils and soil map units, and
predictions (interpretations) of soil behavior for different uses and management.
Soil surveys are the product of a nationwide effort known as the
National Cooperative Soil Survey. Major cooperators in North Dakota are the Soil
Conservation Service (SCS), North Dakota Agricultural Experiment Station, North Dakota
State Soil Conservation Committee, Soil Conservation Districts (SCD), and county
commissions. The SCS provides technical organization required to manage and conduct the
survey. State agencies and land grant universities and many counties provide financial and
technical assistance. In some counties, the Bureau of Land Management, Bureau of Indian
Affairs, United States Forest Service, and various other local boards and districts
provide assistance.
How soil surveys are made
Soil properties are identified on each tract of land in the
survey area. Soil scientists dig holes at various locations on the landscape to examine
the soil. Observations of color, texture, structure, and other characteristics of the
different layers (horizons) are noted. The soil profile (a vertical section of soil
through all horizons) at each hole is compared with other soil profiles in the area. Using
this procedure, the soils are classified, named, and delineated on a map as bodies of soil
in a landscape. Soil scientists observe and record other landscape and cultural features
on the map such as slope gradient, streams, drainageways, lakes, roads, railroads, dams,
and gravel pits.
Modern soil survey began about 1940 with the use of aerial
photographs to study and map soils. Aerial photographs improved soil survey accuracy
compared to methods used prior to 1940. Physical features of land such as drainways,
hills, and depressions are easily seen on aerial photographs and related to soil
properties. Cultural features such as cropping patterns, roads, farmsteads, and railroads
are also shown and help orient the soil scientist when soil boundaries are drawn.
Some samples of soils are collected for laboratory analyses from
sites that represent typical types of soil in the survey area. Soil scientists can relate
the results of the laboratory analyses to those types of soils anywhere in the survey
area. In this way, chemical and physical properties determined in the laboratory are
linked with day-to-day field observations by the soil mapper. Soil maps help the user
estimate soil properties on a parcel of land without actual sampling and testing.
Information contained in soil survey reports
General Information
Information contained in soil survey reports is useful to
producers, private land owners, and a wide variety of professionals that work with natural
resources. Soil mapping requires the soil scientist to utilize information from many other
disciplines. A blend of geology, climatology, agronomy, forestry, range science,
engineering, chemistry, physics, and biology is reflected in soil maps. In addition
to soils information, much of the basic information from the various disciplines
needed for mapping is found within the soil survey report.
Soil Information
General Soil Map:
A general soil map is a small-scale map which gives a broad
picture of the type and distribution of soils that occur in the county or area. Maps of
this scale do not show sufficient detail for comparing the soils on individual tracts or
farms.
Soil Series Descriptions:
Each soil series represents a specific kind of soil with a unique
set of physical, chemical, and mineralogical characteristics. Soils of a specific soil
series also have similar observable properties such as color, texture, structure, and
sequence of soil horizons. The soils within each soil series have similar reactions to use
and management but have uniquely different reactions compared to soils of other soil
series. Soil series usually receive their names from the town or community closest to the
site that represents the typical range of properties for that soil, such as Manfred,
Heimdal, or Fargo. About 264 soil series currently are
recognized in North Dakota.
Soil Map Unit Descriptions:
The separations of area (delineations) on a soil map represent
combinations of soil series that occur in predictable patterns in the landscape. These
predictable combinations are soil map units and are identified by a unique name and
symbol. Some map units represent areas dominated by a single soil series, such as Barnes
loam, 3 to 6 percent slopes. However, many map units represent areas that are dominated by
two or more soil series, such as Barnes - Svea loams, 1 to 6 percent slopes. All soil
areas marked with the same symbol consist of the same combination of soils as identified
in the soil map unit description. Soil map units are named for the one or more soil series
that dominate the unit. A minor percentage of each soil map unit is other soil series that
are not included in the name of the map unit. However, minor soils are discussed in the
map unit description.
Interpretation:
Soil interpretation refers to behavior and response of soils
related to human activities. Interpretations are a guide to use and management of soils in
the survey area. Soils with similar responses to a particular use or treatment often are
grouped together. Common interpretations are land use capability classification, range
site classification, woodland suitability group, engineering classification, wind and
water erodibility groups, and estimated yields of commonly grown crops. Soil
interpretations are generally found in tables and are organized according to map unit
symbol.
Other Soil Data:
The soil survey report also contains information about the
following:
Alkalinity/Acidity
Available water capacity
Degree of erosion
Depth to bedrock
Depth to water table
Horizon thickness
Permeability
Salinity and/or Sodicity
Slope gradient
Soil color
Soil lime (carbonates)
Soil organic matter
Soil structure
Soil texture
Stoniness
Finding information about the soils on your farm or ranch
Soils information about a specific parcel of land can be located
in the soil survey report as follows:
- Refer to the Index to Map Sheets page (usually located just
before the first map sheet). The index directs you to the sheet number (map) of interest.
- Locate the area of interest on the correct map sheet.
- Determine the map units that represent the soils in the area of
interest by comparing map unit symbols to the Soil Legend on the reverse side of
the Index to Map Sheets.
- Refer to the Index to Map Units at the begining of the
report to find the page numbers where these soil map units are described.
- Refer to the Summary of Tables at the beginning of the
report to locate interpretive tables for each soil map unit.
- Use the interpretive tables related to the type of use intended
for the area of interest as a guide for successful management.
How a soil survey report can be of use to you
Agricultural Producers, Farm Managers, and Consultants
The soil survey report contains information that is the basis for
conservation efforts aimed at erosion protection from wind and water. General management
practices that help reduce erosion and maintain soil productivity are discussed for each
soil map unit.
Estimated average yields of the principal crops suited to the
soil and area are given for an above average level of management. Grass and tree species
suited to the soil and area are also discussed. Soil interpretations such as available
water capacity, soil texture, and soil pH can be helpful in making fertilizer
recommendations.
Each map unit is assigned a productivity index for a common crop
grown in the survey area (generally hard red spring wheat in North Dakota). This is a
relative rating between 0 and 100. The productivity index can be converted to expected
yield per acre by multiplying it by the highest yield per acre for the survey area and
dividing the product by 100. Using the productivity index, the producer can refer to the
soils map to determine how productive a particular parcel of land is compared to other
land in the survey area.
Map units are grouped into eight land capability classes that
help categorize land according to its potential for agricultural development. Each class
is defined according to the severity of limitations to agricultural production. All
classes, except for class I, are separated into subclasses according to the type of
limitations.
Classes I - IV have increasing limitations to
cultivation, respectively.
Classes V - VIII are not suitable for
cultivation due to severe limitations.
Soil survey reports of areas proposed for irrigation may contain
a discussion of soil management under irrigation. Irrigation suitability ratings,
limitations, and management problems for each soil are given in those soil survey reports.
Estimated yields under irrigation also are presented. Irrigation potential of each map
unit is provided in all county soil surveys, even though irrigation may not be an
immediate concern.
Sustained production of rangeland depends on proper management.
Soil series are grouped in the soil survey report according to similar native plant
communities and range management needs. Soil - plant community groups are called range
sites and are used to design grazing management plans. Estimated annual rangeland
production is also presented for each soil series in a good, average, and poor year.
Bankers, Investors, Land Appraisers, Credit Agencies and
Directors of Tax Equalization
The soil survey report is a source of information that can be
used to estimate the earning capacity of different soils in the survey area. The
productivity index is an excellent system for rating relative productivity of different
soils. Such information is useful to anyone interested in appraising land for investment,
loan or valuation purposes.
Detailed soil maps and other soil information have been used by
state and local officials in North Dakota and other states as a basis for equalizing land
values for tax purposes.
Natural Resource Education
A county soil survey report is an invaluable source of natural
resource information that can be incorporated into educational programs. Soil is the
result of complex natural processes that are affected by climate, time, geological
materials, topography, and living organisms. Identification and classification of soils
during the mapping process requires accurate information about the environment that
affects soil formation. The soil survey report is, therefore, an excellent inventory of
local natural resources.
Windbreaks, Woodland, and Wildlife
The potential for growing trees is rated in the map unit
descriptions. The preparation and maintenance of wind-break sites are discussed and
species of trees suitable for windbreaks are listed. A limited discussion of native
woodland that includes species and locations is included in the report.
Soil management for wildlife is presented in the report.
Discussion of kinds and distribution of wildlife and methods of improving wildlife habitat
in the survey area are included. Information on degree of soil salinity and occurrence of
water tables is helpful in identifying areas more suited to wildlife than to crops.
Highway/Construction Engineers and Land Developers
Soil information and maps can help highway engineers with the
routing and design of roadways. Soil maps show the areas where construction of road
subgrades by conventional methods may be unsuitable because of unstable soil materials.
Some soil areas are susceptible to frost action unless special precautions are taken
during road construction. Potential sources of sand and gravel for road surfacing and soil
material suitable for top dressing roadside cuts can be located on soil maps. Soil survey
reports can also be used to determine suitability of soils for cross-country movement of
heavy equipment.
Prior knowledge about suitability of soils for construction or
buildings is valuable information to many people, including the homewowner. Land
developers and construction engineers rely on soil survey information to anticipate
general construction and development problems that are common to an area, such as
flooding, high water table, slow permeability, shallow bedrock, soils of low bearing
strength, high shrink-swell soils, or high soil corrosivity. Knowledge of general
engineering problems helps them incorporate remedial measures in their overall development
or construction plans. This information is also useful for planning detailed on-site
investigations prior to construction. Potential construction failures or cost over-runs
can be avoided by consulting a soil survey first.
Planning Boards, Health Officials and Municipal Officials
Soil data on permeability, depth to ground water, flooding, slope
gradient, soil texture, and depth to bedrock can be useful in determining soil suitability
for septic waste filter fields. Septic waste systems will back up and overflow when the
soil does not allow fast enough movement of waste effluent through the filtration field.
Other types of soils allow waste effluent to move too rapidly through the filtration
field, resulting in groundwater contamination. Soil survey information identifies those
soils that may cause serious contamination and health problems due to inadequate
filtration of waste.
Knowledge of local soil capabilities and limitations is useful
when zoning land for various uses. It can help zoning boards prepare land use plans and
zoning maps by evaluating soil suitability for agriculture, private homes, industry,
transportation, and recreation. For example, land areas subject to flooding might be zoned
to prohibit the erection of permanent structures. Soil survey information can also be used
to help officials evaluate proposed building development plans or landfill sites.
New uses and applications of soil survey information
Geographical Information Systems (GIS)
Every scientific discipline must be progressive to meet society's
needs. Soil survey is not an exception. The advent of computers and demand for accurate,
timely soils information have led to the use of geographical information systems (GIS).
Computers allow rapid access to soil maps and interpretive tables. Soil survey information
is just one of many geographical data sets that are part of a GIS. Common data sets used
in a GIS include topography, land use, and hydrology. The different data sets can be
combined, manipulated, and analyzed in many ways. For example, a township board might be
interested in knowing the locations of township roads occurring on soils poorly suited to
road construction. A GIS would allow board members to overlay the township roadmap on the
soil map. Problem areas could be located in a matter of seconds with a GIS. The potential
for GIS as a management tool is limited only by the accuracy of the various data sets and
the imagination of the user.
The National Cooperative Soil Survey is committed to developing a
GIS to meet the growing demand for soils information. The SCS in cooperation with the
State Soil Conservation Committee and North Dakota State University has four GIS work
stations in North Dakota.
Water Resource Vulnerability
Contamination of soils and water resources with industrial,
municipal, and private wastes is a growing concern. Soil acts as a natural filter and
deactivator of many types of contaminants. Filtering efficiency within an area can be
quite variable due to differences in soil properties. Recently, soil scientists have begun
to use information from soil surveys to identify areas of water resource vulnerability. A
general groundwater vulnerabilty map is available for most counties in North Dakota.
Soil interpretations that rate soils series in regard to
contamination from nitrate and different pesticides are being tested. Eventually these
interpretations will be used to provide detailed maps of contamination potential to assist
in managing land to protect water resources. At this time, interpretations for water
resource vulnerability are not in the county soil survey reports.
High Efficiency Application of Agricultural Chemicals
The need for efficient use of agricultural chemicals will
continue to increase due to economic and environmental factors. Recent advances in
computer and control equipment technology are helping to improve efficiency of fertilizer
application.
Actual utilization of fertilizer by the plant varies with changes
in soil properties. Computerized application equipment has been tested that uses soil
survey maps to adjust the application rate of fertilizer. As the equipment moves across a
field, the rate of fertilizer application is automatically adjusted at soil boundaries.
The most advanced application equipment locates itself with respect to soil boundaries by
communicating with a Global Positioning Satelite. Accuracy of location varys with expense
of the positioning system.
Do soil maps have limitations?
Regardless of the purpose and scale of mapping, all map unit
delineations contain small areas of dissimilar soils that cannot be delineated. Most
county soil surveys in North Dakota have been mapped and published at a scale of 1:20,000
or 3.17 inches per mile. Soil maps of this scale can be used to evaluate tracts of land
for most resource planning needs. Soil areas smaller than about five acres cannot be shown
on these maps, even though they differ significantly from the adjacent soils.
On-site investigation is necessary to determine
soil suitability for intensive use of small areas. The capacity of soils on a residential
lot to absorb septic waste effluent or to support the weight of a large building can be
estimated only in a general way from a county soil survey report. On-site soil
examination and testing are required to accurately determine soil suitability for these
and other uses.
For some purposes it is essential that contrasting soil areas of
less than one acre be delineated. The soils of agronomic research sites, for instance,
must be mapped in great detail so that soil conditions can be related to crop performance.
Large-scale maps (8 inches per mile or larger) provide for the delineation of smaller soil
areas.
New information will require periodic updates to all soil survey
reports and maps. Soil mapping is a continual process similar to research in other
scientific disciplines. As soil survey reports age, some parts may rapidly lose their
utility, while other parts may accurately reflect our knowledge for years to come. Updated
soil interpretations can be found at local SCS offices in the Technical Guide.
Soil surveys can help you manage your resources for sustained
productivity
SOIL SURVEYS CAN HELP YOU. They are an inventory of the soils
that affect your basic needs; food, water, and shelter. Soil survey reports provide
information that can be used for agricultural production, environmental protection,
highway and building construction, recreation and wildlife management, and land use
planning and zoning for healthy city and rural environments.
Where to obtain soil survey information
Published county soil survey reports are available at the
respective Soil Conservation Service offices or the Department of Soil Science, North
Dakota State University. For counties with unpublished soil surveys, the local Soil
Conservation Service office should be contacted.
Acknowledgements
The author would like to recognize the contributions of the North
Dakota SCS State Soil Survey staff and North Dakota State Soil Conservation Committee
staff to this publication. Their thorough review of the manuscript was extremely valuable.
Extension Bulletin 60, April
1993
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