HomeMy WebLinkAbout20111188 USDA United States A product of the National Custom Soil Resource
Department of Cooperative Soil Survey,
Agriculture a joint effort of the United Report for
States Department of• 6 HRCS Agriculture and other �►eId Federal agencies, State County,
Natural agencies including the Colorado,
Resources Agricultural Experiment
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Preface
Soil surveys contain information that affects land use planning in survey areas. They
highlight soil limitations that affect various land uses and provide information about
the properties of the soils in the survey areas. Soil surveys are designed for many
different users, including farmers, ranchers, foresters, agronomists, urban planners,
community officials, engineers, developers, builders, and home buyers.Also,
conservationists, teachers, students, and specialists in recreation, waste disposal,
and pollution control can use the surveys to help them understand,protect,or enhance
the environment.
Various land use regulations of Federal, State, and local governments may impose
special restrictions on land use or land treatment. Soil surveys identify soil properties
that are used in making various land use or land treatment decisions.The information
is intended to help the land users identify and reduce the effects of soil limitations on
various land uses.The landowner or user is responsible for identifying and complying
with existing laws and regulations.
• Great differences in soil properties can occur within short distances. Some soils are
seasonally wet or subject to flooding. Some are too unstable to be used as a
foundation for buildings or roads.Clayey or wet soils are poorly suited to use as septic
tank absorption fields. A high water table makes a soil poorly suited to basements or
underground installations.
The National Cooperative Soil Survey is a joint effort of the United States Department
of Agriculture and other Federal agencies, State agencies including the Agricultural
Experiment Stations, and local agencies. The Natural Resources Conservation
Service (NRCS) has leadership for the Federal part of the National Cooperative Soil
Survey.
Information about soils is updated periodically. Updated information is available
through the NRCS Soil Data Mart Web site or the NRCS Web Soil Survey. The Soil
Data Mart is the data storage site for the official soil survey information.
The U.S. Department of Agriculture(USDA)prohibits discrimination in all its programs
and activities on the basis of race, color, national origin, age, disability, and where
applicable, sex, marital status, familial status, parental status, religion, sexual
orientation, genetic information,political beliefs, reprisal,or because all or a part of an
individual's income is derived from any public assistance program. (Not all prohibited
bases apply to all programs.)Persons with disabilities who require alternative means
for communication of program information (Braille, large print, audiotape,etc.)should
contact USDA's TARGET Center at (202) 720-2600 (voice and TDD). To file a
complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400
Independence Avenue, S.W., Washington, D.C. 20250-9410 or call (800)795-3272
(voice)or(202) 720-6382 (TDD). USDA is an equal opportunity provider and
• employer.
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Contents
Preface 2
How Soil Surveys Are Made 4
Soil Map 6
Soil Map (Firestone) 7
Legend (Firestone) 8
Map Unit Legend (Firestone) 9
Map Unit Descriptions (Firestone) 9
Weld County, Colorado, Southern Part Version date:2/11/2008 3:20:37
PM 11
1—Altvan loam, 0 to 1 percent slopes 11
3—Aquolls and Aquents, gravelly substratum 11
27—Heldt silty clay, 1 to 3 percent slopes 13
41—Nunn clay loam, 0 to 1 percent slopes 14
72—Vona loamy sand, 0 to 3 percent slopes 14
73—Vona loamy sand, 3 to 5 percent slopes 15
Soil Information for All Uses 17
• Soil Reports 17
Soil Chemical Properties 17
Chemical Soil Properties (Firestone) 17
Soil Physical Properties 21
Engineering Properties (Firestone) 21
Physical Soil Properties (Firestone) 25
Vegetative Productivity 30
Rangeland Productivity and Plant Composition (Firestone) 30
References 34
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3
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How Soil Surveys Are Made
Soil surveys are made to provide information about the soils and miscellaneous areas
in a specific area.They include a description of the soils and miscellaneous areas and
their location on the landscape and tables that show soil properties and limitations
affecting various uses. Soil scientists observed the steepness, length, and shape of
the slopes;the general pattern of drainage;the kinds of crops and native plants; and
the kinds of bedrock.They observed and described many soil profiles.A soil profile is
the sequence of natural layers, or horizons, in a soil. The profile extends from the
surface down into the unconsolidated material in which the soil formed or from the
surface down to bedrock.The unconsolidated material is devoid of roots and other
living organisms and has not been changed by other biological activity.
Currently,soils are mapped according to the boundaries of major land resource areas
(MLRAs). MLRAs are geographically associated land resource units that share
common characteristics related to physiography, geology, climate, water resources,
soils, biological resources, and land uses (USDA, 2006). Soil survey areas typically
consist of parts of one or more MLRA.
• The soils and miscellaneous areas in a survey area occur in an orderly pattern that is
related to the geology, landforms, relief, climate, and natural vegetation of the area.
Each kind of soil and miscellaneous area is associated with a particular kind of
landform or with a segment of the landform. By observing the soils and miscellaneous
areas in the survey area and relating their position to specific segments of the
landform,a soil scientist develops a concept,or model,of how they were formed.Thus,
during mapping, this model enables the soil scientist to predict with a considerable
degree of accuracy the kind of soil or miscellaneous area at a specific location on the
landscape.
Commonly, individual soils on the landscape merge into one another as their
characteristics gradually change. To construct an accurate soil map, however, soil
scientists must determine the boundaries between the soils. They can observe only
a limited number of soil profiles. Nevertheless, these observations, supplemented by
an understanding of the soil-vegetation-landscape relationship, are sufficient to verify
predictions of the kinds of soil in an area and to determine the boundaries.
Soil scientists recorded the characteristics of the soil profiles that they studied. They
noted soil color, texture, size and shape of soil aggregates, kind and amount of rock
fragments, distribution of plant roots, reaction, and other features that enable them to
identify soils. After describing the soils in the survey area and determining their
properties, the soil scientists assigned the soils to taxonomic classes (units).
Taxonomic classes are concepts. Each taxonomic class has a set of soil
characteristics with precisely defined limits. The classes are used as a basis for
comparison to classify soils systematically. Soil taxonomy, the system of taxonomic
classification used in the United States, is based mainly on the kind and character of
• soil properties and the arrangement of horizons within the profile. After the soil
scientists classified and named the soils in the survey area, they compared the
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Custom Soil Resource Report
individual soils with similar soils in the same taxonomic class in other areas so that
•
they could confirm data and assemble additional data based on experience and
research.
While a soil survey is in progress, samples of some of the soils in the area generally
are collected for laboratory analyses and for engineering tests.Soil scientists interpret
the data from these analyses and tests as well as the field-observed characteristics
and the soil properties to determine the expected behavior of the soils under different
uses. Interpretations for all of the soils are field tested through observation of the soils
in different uses and under different levels of management. Some interpretations are
modified to fit local conditions, and some new interpretations are developed to meet
local needs. Data are assembled from other sources, such as research information,
production records, and field experience of specialists. For example, data on crop
yields under defined levels of management are assembled from farm records and from
field or plot experiments on the same kinds of soil.
Predictions about soil behavior are based not only on soil properties but also on such
variables as climate and biological activity. Soil conditions are predictable over long
periods of time, but they are not predictable from year to year. For example, soil
scientists can predict with a fairly high degree of accuracy that a given soil will have
a high water table within certain depths in most years, but they cannot predict that a
high water table will always be at a specific level in the soil on a specific date.
After soil scientists located and identified the significant natural bodies of soil in the
survey area, they drew the boundaries of these bodies on aerial photographs and
identified each as a specific map unit.Aerial photographs show trees,buildings,fields,
roads, and rivers, all of which help in locating boundaries accurately.
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5
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Soil Map
The soil map section includes the soil map for the defined area of interest, a list of soil
map units on the map and extent of each map unit, and cartographic symbols
displayed on the map.Also presented are various metadata about data used to
produce the map, and a description of each soil map unit.
•
•
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Custom Soil Resource Report
Soil Map (Firestone)
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Custom Soil Resource Report
• Map Unit Legend (Firestone)
. i .;(. . , Wald County,Colorado,Southern Fart(CO616)ri. :: ...
Map Unit Symbot Map Unit Name. Acres inAOl Percept of AOl
1 Altvan loam,0 to 1 percent 139.2 36.3%
slopes
3 Aquolls and Aquents,gravelly 83.3 21.7%
substratum
27 Heldt silty clay,1 to 3 percent 110.3 28.8%
slopes
41 Nunn clay loam,0 to 1 percent 16.4 4.3%
slopes
72 Vona loamy sand,0 to 3 percent 0.0 0.0%
slopes
73 Vona loamy sand,3 to 5 percent 34.0 8.9%
slopes
Totals for Area of Interest(AOI) 383.3 100.0%
Map Unit Descriptions (Firestone)
• The map units delineated on the detailed soil maps in a soil survey represent the soils
or miscellaneous areas in the survey area.The map unit descriptions, along with the
maps, can be used to determine the composition and properties of a unit.
A map unit delineation on a soil map represents an area dominated by one or more
major kinds of soil or miscellaneous areas.A map unit is identified and named
according to the taxonomic classification of the dominant soils. Within a taxonomic
class there are precisely defined limits for the properties of the soils.On the landscape,
however,the soils are natural phenomena,and they have the characteristic variability
of all natural phenomena. Thus,the range of some observed properties may extend
beyond the limits defined for a taxonomic class.Areas of soils of a single taxonomic
class rarely, if ever, can be mapped without including areas of other taxonomic
classes.Consequently,every map unit is made up of the soils or miscellaneous areas
for which it is named and some minor components that belong to taxonomic classes
other than those of the major soils.
Most minor soils have properties similar to those of the dominant soil or soils in the
map unit, and thus they do not affect use and management. These are called
noncontrasting, or similar, components. They may or may not be mentioned in a
particular map unit description. Other minor components, however, have properties
and behavioral characteristics divergent enough to affect use or to require different
management.These are called contrasting,or dissimilar,components.They generally
are in small areas and could not be mapped separately because of the scale used.
Some small areas of strongly contrasting soils or miscellaneous areas are identified
by a special symbol on the maps. If included in the database for a given area, the
• contrasting minor components are identified in the map unit descriptions along with
some characteristics of each. A few areas of minor components may not have been
9
Custom Soil Resource Report
• observed, and consequently they are not mentioned in the descriptions, especially
where the pattern was so complex that it was impractical to make enough observations
to identify all the soils and miscellaneous areas on the landscape.
The presence of minor components in a map unit in no way diminishes the usefulness
or accuracy of the data. The objective of mapping is not to delineate pure taxonomic
classes but rather to separate the landscape into landforms or landform segments that
have similar use and management requirements. The delineation of such segments
on the map provides sufficient information for the development of resource plans. If
intensive use of small areas is planned, however, onsite investigation is needed to
define and locate the soils and miscellaneous areas.
An identifying symbol precedes the map unit name in the map unit descriptions. Each
description includes general facts about the unit and gives important soil properties
and qualities.
Soils that have profiles that are almost alike make up a soil series. Except for
differences in texture of the surface layer, all the soils of a series have major horizons
that are similar in composition,thickness, and arrangement.
Soils of one series can differ in texture of the surface layer, slope, stoniness, salinity,
degree of erosion,and other characteristics that affect their use. On the basis of such
differences, a soil series is divided into soil phases. Most of the areas shown on the
detailed soil maps are phases of soil series. The name of a soil phase commonly
indicates a feature that affects use or management. For example, Alpha silt loam, 0
to 2 percent slopes, is a phase of the Alpha series.
Some map units are made up of two or more major soils or miscellaneous areas.
These map units are complexes, associations, or undifferentiated groups.
•
A complex consists of two or more soils or miscellaneous areas in such an intricate
pattern or in such small areas that they cannot be shown separately on the maps.The
pattern and proportion of the soils or miscellaneous areas are somewhat similar in all
areas. Alpha-Beta complex, 0 to 6 percent slopes, is an example.
An association is made up of two or more geographically associated soils or
miscellaneous areas that are shown as one unit on the maps. Because of present or
anticipated uses of the map units in the survey area, it was not considered practical
or necessary to map the soils or miscellaneous areas separately. The pattern and
relative proportion of the soils or miscellaneous areas are somewhat similar.Alpha-
Beta association, 0 to 2 percent slopes, is an example.
An undifferentiated group is made up of two or more soils or miscellaneous areas that
could be mapped individually but are mapped as one unit because similar
interpretations can be made for use and management. The pattern and proportion of
the soils or miscellaneous areas in a mapped area are not uniform. An area can be
made up of only one of the major soils or miscellaneous areas, or it can be made up
of all of them. Alpha and Beta soils, 0 to 2 percent slopes, is an example.
Some surveys include miscellaneous areas. Such areas have little or no soil material
and support little or no vegetation. Rock outcrop is an example.
•
10
Custom Soil Resource Report
Weld County, Colorado, Southern Part Version date:
2/11/2008 3:20:37 PM
1—Altvan loam, 0 to 1 percent slopes
Map Unit Setting
Elevation:4,500 to 4,900 feet
Mean annual precipitation: 14 to 16 inches
Mean annual air temperature:46 to 48 degrees F
Frost-free period: 130 to 150 days
Map Unit Composition
Altvan and similar soils:90 percent
Minor components: 1 percent
Description of Altvan
Setting
Landform:Terraces
Down-slope shape: Linear
Across-slope shape: Linear
Parent material: Old alluvium
Properties and qualities
Slope:0 to 1 percent
Depth to restrictive feature: More than 80 inches
• Drainage class:Well drained
Capacity of the most limiting layer to transmit water(Ksat): Moderately
high to high (0.20 to 2.00 in/hr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum content:5 percent
Available water capacity: Low (about 5.7 inches)
Interpretive groups
Land capability classification (irrigated): 3s
Land capability(nonirrigated):4e
Ecological site: Loamy Plains (R067BY002CO)
Typical profile
0 to 10 inches: Loam
10 to 25 inches:Clay loam
25 to 60 inches: Gravelly sand
Minor Components
Aquic haplustolls
Percent of map unit: 1 percent
Landform: Swales
3—Aquolls and Aquents, gravelly substratum
• Map Unit Setting
Elevation:4,000 to 7,200 feet
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Custom Soil Resource Report
Mean annual precipitation: 12 to 18 inches
• Mean annual air temperature:45 to 55 degrees F
Frost-free period:80 to 155 days
Map Unit Composition
Aquolls and similar soils: 55 percent
Aquents, gravelly substratum, and similar soils:30 percent
Description of Aquolls
Setting
Landform: Swales, streams, flood plains
Down-slope shape: Linear
Across-slope shape: Linear
Parent material: Recent alluvium
Properties and qualities
Slope: 0 to 3 percent
Depth to restrictive feature: More than 80 inches
Drainage class: Poorly drained
Capacity of the most limiting layer to transmit water(Ksat): Moderately
high to high (0.20 to 2.00 in/hr)
Depth to water table:About 6 to 48 inches
Frequency of flooding: Frequent
Frequency of ponding: None
Maximum salinity: Nonsaline to very slightly saline (0.0 to 4.0 mmhos/
cm)
• Available water capacity: Moderate(about 8.0 inches)
Interpretive groups
Land capability(nonirrigated):6w
Ecological site: Salt Meadow (R067BY035CO)
Typical profile
0 to 48 inches: Loam
48 to 60 inches: Gravelly sand
Description of Aquents, Gravelly Substratum
Setting
Landform: Stream terraces
Down-slope shape: Linear
Across-slope shape: Linear
Parent material: Recent alluvium
Properties and qualities
Slope: 0 to 3 percent
Depth to restrictive feature: More than 80 inches
Drainage class: Poorly drained
Capacity of the most limiting layer to transmit water(Ksat): Moderately
high to very high (0.57 to 19.98 in/hr)
Depth to water table:About 6 to 24 inches
Frequency of flooding: Frequent
Frequency of ponding: None
Calcium carbonate, maximum content: 10 percent
• Maximum salinity: Nonsaline to slightly saline (0.0 to 8.0 mmhos/cm)
Available water capacity: Moderate (about 6.6 inches)
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Custom Soil Resource Report
• Interpretive groups
Land capability classification (irrigated): 6w
Land capability(non irrigated):6w
Ecological site: Salt Meadow (R067BY035CO)
Typical profile
0 to 48 inches:Variable
48 to 60 inches:Very gravelly sand
27—Heldt silty clay, 1 to 3 percent slopes
Map Unit Setting
Elevation:4,950 to 5,050 feet
Mean annual precipitation: 11 to 17 inches
Mean annual air temperature:46 to 59 degrees F
Frost-free period: 110 to 150 days
Map Unit Composition
Heldt and similar soils:85 percent
Description of Heldt
Setting
Landform: Plains
Down-slope shape: Linear
Across-slope shape: Linear
• Parent material: Sediment alluvium derived from shale
Properties and qualities
Slope: 1 to 3 percent
Depth to restrictive feature: More than 80 inches
Drainage class:Well drained
Capacity of the most limiting layer to transmit water(Ksat): Moderately
low to moderately high (0.06 to 0.20 in/hr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum content: 10 percent
Gypsum, maximum content: 1 percent
Maximum salinity: Nonsaline to very slightly saline (0.0 to 4.0 mmhos/
cm)
Sodium adsorption ratio, maximum: 10.0
Available water capacity: High (about 9.6 inches)
Interpretive groups
Land capability classification (irrigated): 3e
Land capability(nonirrigated):4c
Ecological site: Clayey Plains (R067BY042CO)
Typical profile
0 to 7 inches: Silty clay
7 to 60 inches: Silty clay
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Custom Soil Resource Report
41—Nunn clay loam, 0 to 1 percent slopes
Map Unit Setting
Elevation:4,550 to 5,150 feet
Mean annual precipitation: 12 to 18 inches
Mean annual air temperature:46 to 54 degrees F
Frost-free period: 115 to 180 days
Map Unit Composition
Nunn and similar soils: 85 percent
Minor components: 1 percent
Description of Nunn
Setting
Landform: Plains, terraces
Down-slope shape: Linear
Across-slope shape: Linear
Parent material: Mixed alluvium and/or eolian deposits
Properties and qualities
Slope: 0 to 1 percent
Depth to restrictive feature: More than 80 inches
Drainage class:Well drained
Capacity of the most limiting layer to transmit water(Ksat): Moderately
low to moderately high (0.06 to 0.20 in/hr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum content: 15 percent
Maximum salinity: Nonsaline (0.0 to 2.0 mmhos/cm)
Available water capacity: High (about 9.1 inches)
Interpretive groups
Land capability classification (irrigated):2e
Ecological site: Clayey Plains (R067BY042CO)
Typical profile
0 to 9 inches:Clay loam
9 to 29 inches:Clay loam
29 to 60 inches: Sandy loam
Minor Components
Fluvaquentic haplustolls
Percent of map unit: 1 percent
Landform: Swales
72—Vona loamy sand, 0 to 3 percent slopes
Map Unit Setting
Elevation:4,600 to 5,200 feet
Mean annual precipitation: 13 to 15 inches
Mean annual air temperature:48 to 55 degrees F
Frost-free period: 130 to 160 days
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Custom Soil Resource Report
• Map Unit Composition
Vona and similar soils: 85 percent
Minor components: 1 percent
Description of Vona
Setting
Landform:Terraces, plains
Down-slope shape: Linear
Across-slope shape: Linear
Parent material:Alluvium and/or eolian deposits
Properties and qualities
Slope:0 to 3 percent
Depth to restrictive feature: More than 80 inches
Drainage class:Well drained
Capacity of the most limiting layer to transmit water(Ksat): High (1.98
to 6.00 in/hr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum content: 15 percent
Maximum salinity: Nonsaline to very slightly saline (0.0 to 4.0 mmhos/
cm)
Available water capacity: Moderate (about 6.5 inches)
Interpretive groups
•
Land capability classification (irrigated):3e
Land capability(nonirrigated):4e
Ecological site: Sandy Plains (R067BY024CO)
Typical profile
0 to 6 inches: Loamy sand
6 to 28 inches: Fine sandy loam
28 to 60 inches:Sandy loam
Minor Components
Aquic haplustolls
Percent of map unit: 1 percent
Landform: Swales
73—Vona loamy sand, 3 to 5 percent slopes
Map Unit Setting
Elevation:4,600 to 5,200 feet
Mean annual precipitation: 13 to 15 inches
Mean annual air temperature:48 to 55 degrees F
Frost-free period: 130 to 160 days
Map Unit Composition
Vona and similar soils: 85 percent
Minor components: 1 percent
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Custom Soil Resource Report
• Description of Vona
Setting
Landform:Terraces, plains
Down-slope shape: Linear
Across-slope shape: Linear
Parent material:Alluvium and/or eolian deposits
Properties and qualities
Slope:3 to 5 percent
Depth to restrictive feature: More than 80 inches
Drainage class:Well drained
Capacity of the most limiting layer to transmit water(Ksat): High (1.98
to 6.00 in/hr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum content: 15 percent
Maximum salinity: Nonsaline to very slightly saline (0.0 to 4.0 mmhos/
cm)
Available water capacity: Moderate (about 6.5 inches)
Interpretive groups
Land capability classification (irrigated):3e
Land capability(nonirrigated):4e
Ecological site: Sandy Plains (R067BY024CO)
• Typical profile
0 to 6 inches: Loamy sand
6 to 28 inches: Fine sandy loam
28 to 60 inches: Sandy loam
Minor Components
Aquic haplustolls
Percent of map unit: 1 percent
Landform: Swales
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Soil Information for All Uses
Soil Reports
The Soil Reports section includes various formatted tabular and narrative reports
(tables)containing data for each selected soil map unit and each component of each
unit. No aggregation of data has occurred as is done in reports in the Soil Properties
and Qualities and Suitabilities and Limitations sections.
The reports contain soil interpretive information as well as basic soil properties and
qualities. A description of each report(table)is included.
Soil Chemical Properties
• This folder contains a collection of tabular reports that present soil chemical properties.
The reports(tables)include all selected map units and components for each map unit.
Soil chemical properties are measured or inferred from direct observations in the field
or laboratory. Examples of soil chemical properties include pH, cation exchange
capacity, calcium carbonate, gypsum, and electrical conductivity.
Chemical Soil Properties (Firestone)
This table shows estimates of some chemical characteristics and features that affect
soil behavior. These estimates are given for the layers of each soil in the survey area.
The estimates are based on field observations and on test data for these and similar
soils.
Depth to the upper and lower boundaries of each layer is indicated.
Cation-exchange capacity is the total amount of extractable bases that can be held
by the soil, expressed in terms of milliequivalents per 100 grams of soil at neutrality
(pH 7.0)or at some other stated pH value.Soils having a low cation-exchange capacity
hold fewer cations and may require more frequent applications of fertilizer than soils
having a high cation-exchange capacity. The ability to retain cations reduces the
hazard of ground-water pollution.
Effective cation-exchange capacity refers to the sum of extractable bases plus
aluminum expressed in terms of milliequivalents per 100 grams of soil. It is determined
for soils that have pH of less than 5.5.
•
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Custom Soil Resource Report
Soil reaction is a measure of acidity or alkalinity. It is important in selecting crops and
•
other plants, in evaluating soil amendments for fertility and stabilization, and in
determining the risk of corrosion.
Calcium carbonate equivalent is the percent of carbonates, by weight, in the fraction
of the soil less than 2 millimeters in size.The availability of plant nutrients is influenced
by the amount of carbonates in the soil.Incorporating nitrogen fertilizer into calcareous
soils helps to prevent nitrite accumulation and ammonium-N volatilization.
Gypsum is expressed as a percent, by weight, of hydrated calcium sulfates in the
fraction of the soil less than 20 millimeters in size.Gypsum is partially soluble in water.
Soils that have a high content of gypsum may collapse if the gypsum is removed by
percolating water.
Salinity is a measure of soluble salts in the soil at saturation. It is expressed as the
electrical conductivity of the saturation extract, in millimhos per centimeter at 25
degrees C. Estimates are based on field and laboratory measurements at
representative sites of nonirrigated soils. The salinity of irrigated soils is affected by
the quality of the irrigation water and by the frequency of water application. Hence,
the salinity of soils in individual fields can differ greatly from the value given in the
table. Salinity affects the suitability of a soil for crop production, the stability of soil if
used as construction material, and the potential of the soil to corrode metal and
concrete.
Sodium adsorption ratio(SAR)is a measure of the amount of sodium (Na)relative to
calcium (Ca)and magnesium (Mg)in the water extract from saturated soil paste. It is
the ratio of the Na concentration divided by the square root of one-half of the Ca + Mg
concentration. Soils that have SAR values of 13 or more may be characterized by an
• increased dispersion of organic matter and clay particles,reduced saturated hydraulic
conductivity and aeration, and a general degradation of soil structure.
•
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• Soil Physical Properties
This folder contains a collection of tabular reports that present soil physical properties.
The reports(tables)include all selected map units and components for each map unit.
Soil physical properties are measured or inferred from direct observations in the field
or laboratory. Examples of soil physical properties include percent clay, organic
matter, saturated hydraulic conductivity, available water capacity, and bulk density.
Engineering Properties (Firestone)
This table gives the engineering classifications and the range of engineering
properties for the layers of each soil in the survey area.
Depth to the upper and lower boundaries of each layer is indicated.
Texture is given in the standard terms used by the U.S. Department of Agriculture.
These terms are defined according to percentages of sand,silt,and clay in the fraction
of the soil that is less than 2 millimeters in diameter. "Loam,"for example, is soil that
is 7 to 27 percent clay, 28 to 50 percent silt, and less than 52 percent sand. If the
content of particles coarser than sand is 15 percent or more, an appropriate modifier
is added, for example, "gravelly."
Classification of the soils is determined according to the Unified soil classification
system (ASTM, 2005)and the system adopted by the American Association of State
• Highway and Transportation Officials (AASHTO, 2004).
The Unified system classifies soils according to properties that affect their use as
construction material. Soils are classified according to particle-size distribution of the
fraction less than 3 inches in diameter and according to plasticity index, liquid limit,
and organic matter content. Sandy and gravelly soils are identified as GW, GP, GM,
GC, SW, SP, SM, and SC; silty and clayey soils as ML, CL, OL, MH, CH, and OH;
and highly organic soils as PT. Soils exhibiting engineering properties of two groups
can have a dual classification, for example, CL-ML.
The AASHTO system classifies soils according to those properties that affect roadway
construction and maintenance. In this system,the fraction of a mineral soil that is less
than 3 inches in diameter is classified in one of seven groups from A-1 through A-7
on the basis of particle-size distribution, liquid limit,and plasticity index. Soils in group
A-1 are coarse grained and low in content of fines(silt and clay).At the other extreme,
soils in group A-7 are fine grained. Highly organic soils are classified in group A-8 on
the basis of visual inspection.
If laboratory data are available,the A-1, A-2, and A-7 groups are further classified as
A-1-a,A-1-b,A-2-4,A-2-5,A-2-6,A-2-7,A-7-5, or A-7-6.As an additional refinement,
the suitability of a soil as subgrade material can be indicated by a group index number.
Group index numbers range from 0 for the best subgrade material to 20 or higher for
the poorest.
Rock fragments larger than 10 inches in diameter and 3 to 10 inches in diameter are
indicated as a percentage of the total soil on a dry-weight basis.The percentages are
estimates determined mainly by converting volume percentage in the field to weight
• percentage.
21
Custom Soil Resource Report
Percentage (of soil particles)passing designated sieves is the percentage of the soil
•
fraction less than 3 inches in diameter based on an ovendry weight. The sieves,
numbers 4, 10, 40, and 200(USA Standard Series), have openings of 4.76, 2.00,
0.420, and 0.074 millimeters,respectively. Estimates are based on laboratory tests of
soils sampled in the survey area and in nearby areas and on estimates made in the
field.
Liquid limit and plasticity index(Atterberg limits)indicate the plasticity characteristics
of a soil. The estimates are based on test data from the survey area or from nearby
areas and on field examination.
References:
American Association of State Highway and Transportation Officials(AASHTO).2004.
Standard specifications for transportation materials and methods of sampling and
testing. 24th edition.
American Society for Testing and Materials (ASTM). 2005. Standard classification of
soils for engineering purposes.ASTM Standard D2487-00.
•
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Custom Soil Resource Report
• Physical Soil Properties (Firestone)
This table shows estimates of some physical characteristics and features that affect
soil behavior. These estimates are given for the layers of each soil in the survey area.
The estimates are based on field observations and on test data for these and similar
soils.
Depth to the upper and lower boundaries of each layer is indicated.
Particle size is the effective diameter of a soil particle as measured by sedimentation,
sieving,or micrometric methods. Particle sizes are expressed as classes with specific
effective diameter class limits.The broad classes are sand,silt,and clay,ranging from
the larger to the smaller.
Sand as a soil separate consists of mineral soil particles that are 0.05 millimeter to 2
millimeters in diameter. In this table, the estimated sand content of each soil layer is
given as a percentage, by weight, of the soil material that is less than 2 millimeters in
diameter.
Silt as a soil separate consists of mineral soil particles that are 0.002 to 0.05 millimeter
in diameter. In this table, the estimated silt content of each soil layer is given as a
percentage, by weight, of the soil material that is less than 2 millimeters in diameter.
Clay as a soil separate consists of mineral soil particles that are less than 0.002
millimeter in diameter. In this table, the estimated clay content of each soil layer is
given as a percentage, by weight, of the soil material that is less than 2 millimeters in
• diameter.
The content of sand, silt, and clay affects the physical behavior of a soil. Particle size
is important for engineering and agronomic interpretations, for determination of soil
hydrologic qualities, and for soil classification.
The amount and kind of clay affect the fertility and physical condition of the soil and
the ability of the soil to adsorb cations and to retain moisture. They influence shrink-
swell potential, saturated hydraulic conductivity(Ksat), plasticity, the ease of soil
dispersion, and other soil properties. The amount and kind of clay in a soil also affect
tillage and earthmoving operations.
Moist bulk density is the weight of soil(ovendry)per unit volume.Volume is measured
when the soil is at field moisture capacity,that is,the moisture content at 1/3-or 1/10-
bar(33kPa or 10kPa)moisture tension. Weight is determined after the soil is dried at
105 degrees C. In the table, the estimated moist bulk density of each soil horizon is
expressed in grams per cubic centimeter of soil material that is less than 2 millimeters
in diameter. Bulk density data are used to compute linear extensibility, shrink-swell
potential, available water capacity, total pore space, and other soil properties. The
moist bulk density of a soil indicates the pore space available for water and roots.
Depending on soil texture, a bulk density of more than 1.4 can restrict water storage
and root penetration. Moist bulk density is influenced by texture, kind of clay, content
of organic matter, and soil structure.
Saturated hydraulic conductivity(Ksat) refers to the ease with which pores in a
saturated soil transmit water. The estimates in the table are expressed in terms of
micrometers per second.They are based on soil characteristics observed in the field,
particularly structure, porosity, and texture. Saturated hydraulic conductivity (Ksat) is
• considered in the design of soil drainage systems and septic tank absorption fields.
25
Custom Soil Resource Report
Available water capacity refers to the quantity of water that the soil is capable of storing
•
for use by plants. The capacity for water storage is given in inches of water per inch
of soil for each soil layer.The capacity varies, depending on soil properties that affect
retention of water. The most important properties are the content of organic matter,
soil texture, bulk density, and soil structure. Available water capacity is an important
factor in the choice of plants or crops to be grown and in the design and management
of irrigation systems. Available water capacity is not an estimate of the quantity of
water actually available to plants at any given time.
Linear extensibility refers to the change in length of an unconfined clod as moisture
content is decreased from a moist to a dry state. It is an expression of the volume
change between the water content of the clod at 1/3- or 1/10-bar tension (33kPa or
10kPa tension)and oven dryness. The volume change is reported in the table as
percent change for the whole soil. The amount and type of clay minerals in the soil
influence volume change.
Linear extensibility is used to determine the shrink-swell potential of soils.The shrink-
swell potential is low if the soil has a linear extensibility of less than 3 percent;moderate
if 3 to 6 percent; high if 6 to 9 percent; and very high if more than 9 percent. If the
linear extensibility is more than 3, shrinking and swelling can cause damage to
buildings, roads, and other structures and to plant roots. Special design commonly is
needed.
Organic matter is the plant and animal residue in the soil at various stages of
decomposition. In this table, the estimated content of organic matter is expressed as
a percentage, by weight,of the soil material that is less than 2 millimeters in diameter.
The content of organic matter in a soil can be maintained by returning crop residue to
the soil.
• Organic matter has a positive effect on available water capacity,water infiltration,soil
organism activity, and tilth. It is a source of nitrogen and other nutrients for crops and
soil organisms.
Erosion factors are shown in the table as the K factor(Kw and Kf)and the T factor.
Erosion factor K indicates the susceptibility of a soil to sheet and rill erosion by water.
Factor K is one of six factors used in the Universal Soil Loss Equation(USLE)and the
Revised Universal Soil Loss Equation (RUSLE)to predict the average annual rate of
soil loss by sheet and rill erosion in tons per acre per year. The estimates are based
primarily on percentage of silt,sand,and organic matter and on soil structure and Ksat.
Values of K range from 0.02 to 0.69. Other factors being equal, the higher the value,
the more susceptible the soil is to sheet and rill erosion by water.
Erosion factor Kw indicates the erodibility of the whole soil.The estimates are modified
by the presence of rock fragments.
Erosion factor Kf indicates the erodibility of the fine-earth fraction,or the material less
than 2 millimeters in size.
Erosion factor T is an estimate of the maximum average annual rate of soil erosion by
wind and/or water that can occur without affecting crop productivity over a sustained
period. The rate is in tons per acre per year.
Wind erodibility groups are made up of soils that have similar properties affecting their
susceptibility to wind erosion in cultivated areas.The soils assigned to group 1 are the
most susceptible to wind erosion, and those assigned to group 8 are the least
susceptible. The groups are described in the "National Soil Survey Handbook."
• Wind erodibility index is a numerical value indicating the susceptibility of soil to wind
erosion, or the tons per acre per year that can be expected to be lost to wind erosion.
26
Custom Soil Resource Report
• There is a close correlation between wind erosion and the texture of the surface layer,
the size and durability of surface clods, rock fragments, organic matter, and a
calcareous reaction. Soil moisture and frozen soil layers also influence wind erosion.
Reference:
United States Department of Agriculture, Natural Resources Conservation Service.
National soil survey handbook, title 430-VI. (http://soils.usda.gov)
•
•
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Custom Soil Resource Report
• Vegetative Productivity
This folder contains a collection of tabular reports that present vegetative productivity
data. The reports (tables) include all selected map units and components for each
map unit.Vegetative productivity includes estimates of potential vegetative production
for a variety of land uses, including cropland, forestland, hayland, pastureland,
horticulture and rangeland. In the underlying database, some states maintain crop
yield data by individual map unit component. Other states maintain the data at the
map unit level.Attributes are included for both,although only one or the other is likely
to contain data for any given geographic area. For other land uses, productivity data
is shown only at the map unit component level. Examples include potential crop yields
under irrigated and nonirrigated conditions, forest productivity, forest site index, and
total rangeland production under of normal, favorable and unfavorable conditions.
Rangeland Productivity and Plant Composition
(Firestone)
In areas that have similar climate and topography, differences in the kind and amount
of rangeland or forest understory vegetation are closely related to the kind of soil.
Effective management is based on the relationship between the soils and vegetation
and water.
• This table shows, for each soil that supports vegetation suitable for grazing, the
ecological site; the total annual production of vegetation in favorable, normal, and
unfavorable years;the characteristic vegetation; and the average percentage of each
species. An explanation of the column headings in the table follows.
An ecological site is the product of all the environmental factors responsible for its
development. It has characteristic soils that have developed over time throughout the
soil development process;a characteristic hydrology,particularly infiltration and runoff
that has developed over time;and a characteristic plant community(kind and amount
of vegetation). The hydrology of the site is influenced by development of the soil and
plant community. The vegetation, soils, and hydrology are all interrelated. Each is
influenced by the others and influences the development of the others. The plant
community on an ecological site is typified by an association of species that differs
from that of other ecological sites in the kind and/or proportion of species or in total
production. Descriptions of ecological sites are provided in the Field Office Technical
Guide, which is available in local offices of the Natural Resources Conservation
Service (NRCS).
Total dry-weight production is the amount of vegetation that can be expected to grow
annually in a well managed area that is supporting the potential natural plant
community. It includes all vegetation,whether or not it is palatable to grazing animals.
It includes the current year's growth of leaves,twigs,and fruits of woody plants. It does
not include the increase in stem diameter of trees and shrubs. It is expressed in pounds
per acre of air-dry vegetation for favorable, normal, and unfavorable years. In a
favorable year,the amount and distribution of precipitation and the temperatures make
growing conditions substantially better than average. In a normal year, growing
conditions are about average. In an unfavorable year, growing conditions are well
• below average, generally because of low available soil moisture. Yields are adjusted
to a common percent of air-dry moisture content.
30
Custom Soil Resource Report
• Characteristic vegetation (the grasses, forbs, and shrubs that make up most of the
potential natural plant community on each soil)is listed by common name. Under
rangeland composition, the expected percentage of the total annual production is
given for each species making up the characteristic vegetation. The amount that can
be used as forage depends on the kinds of grazing animals and on the grazing season.
Range management requires knowledge of the kinds of soil and of the potential natural
plant community. It also requires an evaluation of the present range similarity index
and rangeland trend. Range similarity index is determined by comparing the present
plant community with the potential natural plant community on a particular rangeland
ecological site. The more closely the existing community resembles the potential
community, the higher the range similarity index. Rangeland trend is defined as the
direction of change in an existing plant community relative to the potential natural plant
community. Further information about the range similarity index and rangeland trend
is available in the"National Range and Pasture Handbook,"which is available in local
offices of NRCS or on the Internet.
The objective in range management is to control grazing so that the plants growing
on a site are about the same in kind and amount as the potential natural plant
community for that site. Such management generally results in the optimum
production of vegetation, control of undesirable brush species, conservation of water,
and control of erosion. Sometimes, however, an area with a range similarity index
somewhat below the potential meets grazing needs, provides wildlife habitat, and
protects soil and water resources.
Reference:
United States Department of Agriculture, Natural Resources Conservation Service,
• National range and pasture handbook.
•
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