United States

Department of

Agriculture

Natural

Resources

Conservation

Service

From the 

Surface Down

An Introduction to Soil Surveys

for Agronomic Use

Second Edition
Credits

Cover photo courtesy of Frankie F. Wheeler and Larry Ratliff, retired soil scientists.

Figures 1, 2, 12, 21, 22, 23, 27, and 28 created by the U.S. Department of Agriculture, 

Natural Resources Conservation Service (or Soil Conservation Service).

Figures 3, 4, 5, 6, 7, 8, 13, 14, 15, and 20 reprinted from Soils of the Great Plains, 

by Andrew R. Aandahl, by permission from the University of Nebraska Press. 

Copyright 1982 by the University of Nebraska Press.

Figures 9 and 19 courtesy of Edgar White, Natural Resources Conservation Service, 

Harrisburg, PA.

Figure 10 courtesy of John Kimble, retired soil scientist.

Figures 11, 16, 17, 18, and 25 are from the author’s (William Broderson’s) collection.

Figure 24 created from Evaluating Missouri Soils, by Dr. C.L. Scrivner and James C. 

Baker. Circular 915, Extension Division, University of Missouri-Columbia. 

Figure 26 courtesy of Douglas Wysocki, Natural Resources Conservation Service, 

Lincoln, NE. 

Cover

Profile of Segno fine sandy loam, a Plinthic Paleudalf. Note the characteristic blocks of 

plinthite at a depth of 30 inches.

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First edition printed in1991;

revised in1994, 2001, and 2003

Second edition printed in 2010
Contents

Introduction....................................................................................................................1

Section 1: What are soil horizons?............................................................................2

Section 2: How is soil formed?..................................................................................7

Section 3: What are the soil-forming processes?....................................................11

Soil survey information ................................................................................................14

Section 4: Soil properties ........................................................................................14

Section 5: Management interpretations ..................................................................20

Section 6: General soil information .........................................................................23

Section 7: Detailed soil information.........................................................................26

Location of information ................................................................................................27

Section 8: Location of soil properties and interpretations .......................................27

References ..................................................................................................................30

Many of our life’s activities and pursuits are

 related to and influenced by the behavior

 of the soil around our houses, roads, 

septic and sewage disposal systems, airports, parks, 

recreation sites, farms, forests, schools, and shopping 

centers. What is put on the land should be guided by 

the soil that is beneath it.

Like snowflakes, no two soils are exactly the same. 

Surface and subsurface soil features change across 

landscapes (fig. 1). A grouping of soils having similar 

properties and similar behavioral characteristics is 

called a series. A series generally is named for a town 

or local landmark. For example, the Mexico series is 

named for a town in north-central Missouri. More than 

21,300 soil series and 285,200 soil map units have 

been named and described in the United States, and 

more are being defined each year. 

When soils are mapped, soil series are further 

divided into phases according to properties that are 

important to soil use, such as texture of the surface 

layer and slope. These phases of soil series all have a 

characteristic behavior. The behavior of the individual 

phase is applicable no matter where the soil is 

observed.

One of the main references that can help land 

users determine the potentials and limitations of soils 

is a soil survey. The “List of Surveys by State” (http://

soils.usda.gov/survey/printed_surveys/) indicates the 

availability of soil survey information in paper copies, 

in PDF files on CD or on the Web, and in tables and 

reports in Web Soil Survey (http://websoilsurvey.nrcs.

usda.gov/). A soil survey is prepared by soil scientists 

who determine the properties of soil and predict soil 

behavior for a host of uses. These predictions, often 

called soil interpretations, are developed to help users 

of soils manage the resource.

A soil survey generally includes soils data for one 

county, parish, or other geographic area. During a soil 

survey, soil scientists walk over the landscapes, bore 

holes with soil augers, and examine cross sections 

of soil profiles. They determine the texture, color, 

structure, and reaction of the soil and the relationship 

and thickness of the different soil horizons. Some soils 

are sampled and tested at soil survey laboratories for 

certain soil property determinations, such as cationexchange capacity and bulk density.

The intent of this publication is to increase user 

understanding of soils and of the content of soil 

surveys and supplemental interpretations that are 

important to agronomic programs.

Proficiency in using soil survey data requires 

a basic understanding of the concepts of soil 

development and of soil-landscape relationships. 

These topics are covered briefly in the next three 

sections.

From the Surface Down

An Introduction to Soil Surveys for

Agronomic Use, Second Edition

United States Department of Agriculture, Natural Resources Conservation Service, 

Soil Survey Staff 1

1First edition (1991) by William D. Broderson, retired soil scientist. Sections 7 and 8 in the second edition (2010) by Jim R. Fortner, soil 

scientist, USDA, Natural Resources Conservation Service, National Soil Survey Center, Lincoln, Nebraska.

Introduction

Figure 1.—Facts about soil.


Section 1: What are soil horizons?

Soils form in bedrock residuum or in material

 deposited by ice, wind, water, or gravity.

 Layers, called horizons, form over time in the 

soils. These layers are evident where roads have been 

cut through hills or streams have scoured through 

valleys and in other areas where the soil is exposed.

Where soil-forming factors are favorable, five or six 

master horizons may be in a mineral soil profile (fig. 

2). Each master horizon is subdivided into specific 

layers that have a unique identity. The thickness 

of each layer varies with location. Under disturbed 

conditions, such as intensive agriculture, or where 

erosion is severe, not all horizons will be present. 

Young soils have fewer major horizons. An example is 

the bottom-land soil in figure 12 (shown in section 2, 

page 7) and the deep loess soil in figure 3.

The uppermost layer in an undisturbed soil may 

be an organic horizon, or O horizon. It consists 

of fresh and decaying plant residue from such 

sources as leaves, needles, twigs, moss, lichens, 

and other organic material. Some organic materials 

were deposited under water (figs. 4 and 5). The 

subdivisions Oa, Oe, and Oi are used to identify levels 

of decomposition. The O horizon is dark because of 

large amounts of accumulated humus.

Below the O horizon is the A horizon. The A horizon 

is mainly mineral material. It is generally darker than 

the lower horizons because of varying amounts of 

humified organic matter (figs. 6 and 7). This horizon 

is where most root activity occurs and generally is 

the most productive layer of soil. It may be referred to 

Figure 2.—A soil profile with five major horizons. as a surface layer in a soil survey. An A horizon that 

Figure 3.—Somewhat excessively drained Colby 

soil formed in loess. A horizon (0 to 8 inches) 

of grayish brown silt loam; AC horizon (8 

to 16 inches) of pale brown silt loam; C 

horizon (below 16 inches) of pale brown silt 

loam. Aridic Ustorthent. Western Nebraska, 

eastern Colorado, Kansas, South Dakota, and 

Wyoming. 
has been buried beneath more recent deposits is 

designated as an “Ab” horizon (fig. 4).

The E horizon generally is bleached or whitish 

(figs. 8, 9, and 10). As water moves down through this 

horizon, soluble minerals and nutrients dissolve and 

some dissolved materials are washed (leached) out. 

The main feature of this horizon is the loss of silicate 

clay, iron, aluminum, humus, or some combination of 

Figure 4.—Poorly drained Cathro soil. Thick Oa 

and Oe horizons (0 to 37 inches) of organic 

material developed from a continuous high 

water table. A buried 2Ab horizon (37 to 45 

inches) of black loam. Terric Haplosaprist. 

Northeastern Minnesota, northern Wisconsin, 

northern Michigan, and upper New England.

these, leaving a concentration of silica sand and silt 

particles.

Below the A or E horizon is the B horizon, or 

subsoil (figs. 6 and 8). The B horizon generally is 

lighter colored, denser, and lower in content of 

organic matter than the A horizon. It commonly is 

the zone where leached materials accumulate. The 

B horizon is further characterized by the materials 

that make up the accumulation. In a Bt horizon, for 

example, clay has accumulated. This accumulation 

is indicated by the letter “t” in the horizon designator. 

Other illuvial concentrations or accumulations include 

iron, aluminum, humus, carbonates, gypsum, and 

silica. A B horizon that does not have recognizable 

concentrations but has color or structure different from 

those of adjacent horizons is called a Bw horizon.

Still deeper in the profile is the C horizon, or 

substratum (fig. 3). The C horizon may consist of 

material with less clay than the overlying horizons, 

or it may consist of other less weathered sediments. 

Partially disintegrated parent material and mineral 

particles are in this horizon. Some soils have a soft 

bedrock horizon that is given the designation Cr (fig. 

11). A C horizon described as 2C consists of different 

material, generally of an older age than the horizons 

that overlie it.

The lowest horizon, the R horizon, is bedrock (fig. 

11). Bedrock can be within a few inches of the surface 

or many feet below the surface. Where bedrock is very 

deep and below the normal depths of observation, an 

R horizon is not described.

Figure 5.—Surface of a very poorly drained soil that has 

many depressions.
Figure 6.—Moderately well drained Pawnee soil formed in till. 

The A horizon is 14 inches thick. The Bt horizon, between 

depths of 14 and 32 inches, is dark brown clay that has 

prismatic structure. Pockets of white, soft lime are at a 

depth of 53 inches. Oxyaquic Vertic Argiudoll. Nebraska 

and northeastern Kansas.

Figure 7.—Well drained Ferris soil. The A horizon is olive clay 

about 6 inches thick. Pale olive clay is between depths 

of 6 and 60 inches. Cracks are filled with surface soil 

material to a depth of 24 inches. Chromic Udic Haplustert. 

Texas and Oklahoma.
Figure 9.—Moderately well drained Exum soil formed in loamy 

Coastal Plain sediments. A grayish brown A horizon (0 

to about 6 inches); a light brownish gray E horizon (6 to 

10 inches); thick, yellowish brown, very strongly acid Bt 

horizons to a depth of 6 feet. Aquic Paleudult. Maryland, 

North Carolina, South Carolina, and Virginia.

Figure 8.—Well drained Wallace soil formed in sandy deposits 

on old sand dunes, lake benches, and outwash plains. 

This soil has an A horizon (0 to about 2 inches) of dark 

grayish brown sand; an E horizon (2 to 10 inches) of 

white sand; and a Bhsm horizon (10 to 26 inches) of dark 

reddish brown, brown, and yellowish brown, massive 

and cemented ortstein. The B horizon has illuvial 

concentrations of organic matter, aluminum, and iron. 

Typic Durorthod. Northern Michigan and New York.
Figure 10.—Poorly drained Felda soil formed in sandy marine 

material. A grayish brown and light gray E horizon is 

between depths of 5 and 24 inches. An irregular boundary 

is between the E horizon and the Bt horizon, which is at a 

depth of 24 inches. Arenic Endoaqualf. Florida.

Figure 11.—Well drained Hambright soil formed in amorphous 

material derived from basic igneous rocks. The content of 

rock fragments is about 50 percent to the Cr horizon, at 

a depth of 15 inches. Fractured basalt (R horizon) is at a 

depth of 19 inches. Lithic Haploxeroll. California.
Section 2: How is soil formed?

Figure 12 shows common landscapes. Soils

 form through the interactions of climate,

 living organisms, and landscape position as 

they influence the decomposition and transformation 

of parent material over time. Figure 12 shows how 

soil profiles change from weakly developed to well 

developed with time. Generally, soils on older terraces 

or second bottoms have a developed B horizon, 

unlike recent soils on first bottoms. The recent soils 

may have strata varying in thickness, texture, and 

composition and may have begun accumulating 

humus in the surface layer.

Differences in climate, parent material, landscape 

position, and living organisms from one location to 

another and the amount of time the material has been 

in place all influence the soil-forming process.

Five soil-forming factors

Parent material

Climate

Living organisms

Landscape position

Time

Parent material

Parent material refers to the great variety of 

unconsolidated organic material (such as fresh peat) 

and mineral material in which soil formation begins. 

Mineral material includes partially weathered rock; ash 

from volcanoes; sediments moved and deposited by 

wind, water, or gravity; and ground-up rock deposited 

by glacial ice. The material has a strong effect on 

the type of soil that forms and the rate at which it 

forms. Soil formation may take place more quickly in 

materials that are more permeable to water (fig. 8). 

Dense, massive, clayey materials can be resistant to 

the processes of soil formation (fig. 7). In soils that 

formed in sandy material, the A horizon may be a 

little darker than its parent material, but the B horizon 

tends to have a similar color, texture, and chemical 

composition (fig. 13).

Climate

Climate is a major factor in determining the kind of 

plant and animal life on and in the soil. It determines 

the amount of water available for weathering minerals 

and for transporting the minerals and elements 

released.

Figure 12.—Landscape position, climate, time, living organisms, and parent material influence soil 

formation.
The soil in figure 14 formed in drier regions than 

the soil in figure15. Through its influence on soil 

temperature, climate determines the rate of chemical 

weathering.

Figure 13.—Well drained Brownfield soil formed 

in old eolian material. Light brown fine sand 

(0 to 30 inches) over red and yellowish red 

sandy clay loam (30 to 60 inches). Arenic 

Aridic Paleustalf. New Mexico and Texas. 

Figure 14.—Well drained Clovis soil formed in thick, 

loamy sediments on fans and plains of old alluvium. 

The accumulation of calcium carbonate increases 

with depth, beginning at a light brown loam Bk 

horizon at 10 inches. Ustic Calciargid. New Mexico, 

east-central Arizona, and southwestern Utah.
Figure 15.—Well drained Olton soil formed in mixed alluvial 

and eolian material. Ap horizon (0 to 6 inches) of brown 

loam; Bt horizon (6 to 32 inches) of reddish brown clay 

loam; whitish calcium carbonate below the Bt horizon. 

Aridic Paleustoll. Texas and New Mexico high plains.

Warm, moist climates encourage rapid plant 

growth and thus high organic-matter production. 

Also, they accelerate organic-matter decomposition. 

The opposite is true for cold, dry climates. Under the 

control of climate, freezing, thawing, wetting, and 

drying break parent material apart.

Rainfall causes leaching. Rain dissolves some 

minerals, such as carbonates, and transports them 

deeper into the soil. Some acid soils formed in parent 

material that originally contained limestone. Rainfall 

can also be acid, especially downwind from industrial 

processes.

Living organisms

Plants affect soil formation by supplying upper 

layers with organic matter, recycling nutrients from 

lower to upper layers, and helping to control erosion. 

In general, deep-rooted plants contribute more to soil 

formation than shallow-rooted plants because the 

passages they create allow greater water movement, 

which in turn aids in leaching. Leaves, twigs, and bark 

from large plants fall onto the soil and are broken 

down by fungi, bacteria, insects, earthworms, and 

burrowing animals. These organisms eat and break 

down organic matter, releasing plant nutrients. Some 

change certain elements, such as sulfur and nitrogen, 

into usable forms for plants.

Microscopic organisms and the humus they 

produce act as a kind of glue, holding soil particles 

together in aggregates. Well-aggregated soil provides 

the right combination of air and water to plant roots.

Landscape position

Landscape position causes local changes in 

moisture and temperature. When rain falls on a 

landscape, water begins to move downward by the 

force of gravity, either through the soil or across 

the surface to a lower elevation. In an area where 

climate, living organisms, parent material, and time 

are held constant, the drier upslope soils may be quite 

different from the wetter soils at the base of the slope, 

where water accumulates. The wetter soils may have 

reducing conditions that will inhibit proper root growth 

for plants that require a balance of soil oxygen, water, 

and nutrients.

The steepness, shape, and length of slopes are 

important because they influence the rate at which 

water flows into or off the soil. If unprotected, the more 

sloping soils may become eroded and thus have a 

thinner surface layer. Eroded soils tend to be less 

fertile and have less available water than uneroded 

soils of the same series.
10

Aspect affects soil temperature and moisture. In 

most of the continental United States, soils on northfacing slopes tend to be cooler and wetter than soils 

on south-facing slopes. These differences affect 

seedling emergence and the rate of plant growth. 

Soils on north-facing slopes tend to have thicker A 

and B horizons.

Time

Time is required for horizon formation. The longer a 

soil surface has been exposed to soil-forming agents, 

such as rain and growing plants, the greater the 

development of the soil profile. Soils in areas of recent 

alluvial or windblown material and soils on steep 

slopes where erosion has been active may show very 

little evidence of horizon development (fig. 3).

Soils on the older, stable surfaces generally 

have well defined horizons because the rate of soil 

formation has exceeded the rate of geologic erosion 

or deposition (fig. 6). As soils age, many original 

minerals are destroyed. Many new ones are formed. 

Soils become more leached, more acid, and more 

clayey. In many well drained soils, the B horizons tend 

to become redder as iron accumulates with time (figs. 

8 and 15).
11

The four major processes that change parent

 material into soil are additions, losses, 

 translocations, and transformations.

Section 3: What are the soil-forming processes?

Additions

The most obvious addition is the accumulation 

of organic matter. As soon as plants begin to grow 

in fresh parent material, organic matter begins to 

accumulate. Organic matter gives a black or dark 

brown color to the surface layer (fig. 6). Even young 

soils may have a dark surface layer (fig. 3). Most 

additions of organic matter to the surface increase 

the cation-exchange capacity and the supply and 

availability of plant nutrients.

Additions may occur during periods of rainfall or 

during periods when eolian (windblown) material is 

deposited (fig. 13). On the average, rainfall adds about 

5 pounds of nitrogen per acre per year. It also adds 

other elements and fine mineral particles. By causing 

rivers to flood, rainfall is indirectly responsible for the 

addition of new sediment to the soil on a flood plain.

Other additions occur via gravity in areas where 

soils creep or are eroded. Soil material from these 

areas is deposited in downslope areas.

Losses

Most losses occur through leaching. Water moving 

through the soil dissolves certain minerals and 

transports them into deeper layers. Some materials, 

especially sodium salts, gypsum, and calcium 

carbonate, are relatively soluble (figs. 14, 15, and 

16). They are removed early during soil formation. 

Carbonates generally are removed from the upper 

horizons of soils in humid regions or are leached out 

of the soils entirely. Quartz, aluminum, iron oxides, 

and kaolinitic clay weather slowly. They become the 

main components of highly weathered soil.

Fertilizers are relatively soluble, and many, such 

as nitrogen and potassium, are readily lost through 

Processes of soil formation

Additions

Losses

Translocations

Transformations

leaching caused either by natural rainfall or by 

irrigation water. Long-term use of fertilizers based on 

ammonium may acidify the soil and contribute to the 

loss of carbonates in some areas.

Oxygen is a gas that is released into the 

atmosphere by growing plants. Carbon dioxide is 

consumed by the growing plants, but it is lost from 

the soil as fresh organic matter decays. When soil is 

wet, nitrogen can be changed to a gas and lost to the 

atmosphere.

Solid mineral and organic particles are lost through 

erosion. Such losses can be serious because the 

material lost is generally from the most productive part 

of the soil profile. On the other hand, the sediment 

Figure 16.—Somewhat poorly drained Salmo soil, which has 

strata of alluvial material with textures of fine sandy loam 

and silt loam (0 to 18 inches) and has an accumulation of 

soluble salts at a depth of 24 inches. Cumulic Endoaquoll. 

South Dakota and Nebraska. 
12

relocated to the lower slope positions or deposited on 

bottom lands can increase or decrease the productive 

use of the soils in those areas.

Translocations

Translocation is the movement of soil material from 

one place to another. In areas of low rainfall, leaching 

often is incomplete. Water starts moving down through 

the soil, dissolving soluble minerals as it goes. There 

is not enough water, however, to move the minerals 

all the way through the soil. When the water stops 

moving and then evaporates, salts are left behind. Soil 

layers with accumulations of calcium carbonate or 

other salts form in this way. If this cycle occurs enough 

times, a calcareous hardpan can form.

Upward translocation and lateral movement occur 

in some soils. Low-lying soils can have a high water 

table, even if they are in dry areas. Evaporation at the 

surface causes water to move upward (fig. 16). Salts 

are dissolved on the way. They are deposited on the 

surface as the water evaporates (fig. 17).

Transformations

Transformations are changes that take place in 

the soil. Micro-organisms that live in the soil feed 

on fresh organic matter and change it into humus. 

Chemical weathering changes the parent material. 

Some minerals are destroyed completely. Others are 

changed into new minerals. Many of the clay-sized 

particles in soil are actually new minerals that form 

during soil development.

Other transformations can change the form of 

certain materials. Iron oxides (ferric form) usually 

give soils a yellowish or reddish color. In waterlogged 

soils, however, iron oxides lose some of their oxygen 

and are considered reduced. The reduced form of 

iron (ferrous) is easily removed from the soil through 

leaching. After the iron is gone, the leached zone 

generally is grayish or whitish (fig. 8).

Repeated cycles of saturation and drying create 

mottles (splotches of colored soil in a matrix of a 

different color). Part of the soil is gray because iron 

oxide is reduced or lost, and the part in which the iron 

oxide is not removed or reduced is browner (figs. 18 

and 19). During long periods of saturation, gray-lined 

root channels develop. These may indicate a possible 

loss of iron caused by enhanced microbial activity 

following an addition of humus from decayed roots.

Figure 17.—Salinity-alkalinity problem caused by poor internal 

soil drainage. California.

Figure 18.—Munsell soil color. The soil block on the left has 

gray reduced colors. The one on the right has reddish 

oxidized colors.
13

Figure 19.—Moderately well drained Mattapex soil, wet phase, 

formed in marine sediments. Dark grayish brown A horizon 

(0 to 6 inches); brown BE horizon (6 to 12 inches); yellowish 

brown, strongly acid Bt horizon (12 to 36 inches). Common 

light brownish gray mottles are in the part of the Bt horizon 

between depths of 21 and 36 inches. A C horizon is at a depth 

of 36 inches. Aquic Hapludult. Maryland, Delaware, Virginia, 

and New Jersey. 
14

Section 4: Soil properties

Soil survey publications describe a number 

 of properties that pertain to agriculture. 

 Some properties, such as slope gradient 

and factors K and T, relate to erosion. Others relate 

to plant growth. These include depth to layers that 

restrict root development, available water capacity, 

salinity, and the capacity of the soil to retain and 

release plant nutrients. Some properties relate to the 

ability of the soil to retain soluble substances that may 

cause pollution of ground water. These include organic 

matter and pH, which affects the need for additions of 

lime. Alteration of some properties, such as slope, can 

improve the suitability of a site. For example, properly 

constructed terraces can shorten the slope length and 

thus reduce the hazard of erosion or the grade for 

irrigation. The following paragraphs describe the major 

soil properties that affect the suitability of a soil for a 

number of specific uses.

Available water capacity (AWC)

Available water capacity is an estimate of how 

much water a soil can hold and release for use by 

most plants, measured in inches of water per inch of 

soil. AWC is influenced by soil texture, content of rock 

fragments, depth to a root-restrictive layer, organic 

matter, and compaction. It is used in scheduling 

irrigation and in determining plant populations. The 

type of soil structure can influence the availability of 

water to plants and the rate at which water is released 

to plant roots. A soil with a tillage pan may not allow 

roots to penetrate and extract the deeper water.

Bedrock and other restrictive layers

There are 20 kinds of restrictive layers recognized 

in soil surveys. Examples are cemented pans, 

permafrost, dense layers, layers with excessive 

sodium or salts, and bedrock. 

Bedrock is the solid rock under the soil and parent 

material (fig. 11). In areas where it is exposed at 

the surface, it is referred to as rock outcrop. The 

depth from the soil surface to bedrock influences the 

potential of the soil for plant growth and agronomic 

practices. Soft bedrock consists of material that 

can be ripped. A shallow depth to bedrock results 

in a lower available water capacity and thus drier 

conditions for plants. It also restricts the rooting depth.

Five depth classes are defined for use in soil 

surveys (table 1).

Table 1.—Depth classes

Very shallow ................................ Less than 10 inches

Shallow................................................10 to 20 inches

Moderately deep..................................20 to 40 inches

Deep....................................................40 to 60 inches

Very deep ....................................More than 60 inches

Calcium carbonate

Calcium carbonate (CaCO3

) influences the 

availability of plant nutrients, such as phosphorus 

and molybdenum. Iron, boron, zinc, and manganese 

deficiencies are common in plants grown in soils 

that have significant levels of calcium carbonate 

equivalent, especially in the surface layer. Soil texture 

influences the levels at which these deficiencies 

commonly occur. Sensitive crops may show 

deficiencies even at low levels (0.5 to 2.0 percent).

Cation-exchange capacity (CEC)

Cation-exchange capacity is the ability of a soil 

to hold and exchange cations. It is one of the most 

important chemical properties in soil and generally 

is closely related to soil fertility. A few of the plant 

nutrient cations include calcium, magnesium, 

potassium, iron, and ammonium.

Generally, as CEC levels decrease, more frequent 

and smaller applications of fertilizer are desirable. 

Smaller applications of fertilizer on soils that have low 

CEC levels may reduce fertilizer loss to surface and 

ground waters, lessening the impact on water quality. 

In many highly weathered, naturally acid soils, CEC is 

lower when pH is lower and higher when pH is higher.

Drainage class (natural)

Drainage class refers to the depth, frequency, and 

duration of periods of saturation or partial saturation 

during soil formation. Seven classes of natural 

drainage are used in soil surveys. They range from 

excessively drained to very poorly drained (fig. 5).

Erosion factor (K)

The soil erosion factor (Kf and Kw) is a relative 

index of the susceptibility of bare, cultivated soil to 

particle detachment and removal and transport by 

rainfall. It can be computed from particle size, organic 

matter, saturated hydraulic conductivity, and structure. 

K values range from 0.02 to 0.64 or more. The 

higher the value, the greater the susceptibility. Soils 

Soil Survey Information

Sections 4 through 7 describe the agronomic soil information published in soil surveys or contained in the Field 

Office Technical Guide of the Natural Resources Conservation Service.
15

that have more silt and very fine sand are generally 

more erodible than other soils because of weaker 

bonding. Kf is adjusted downward for the percent of 

rock fragments in each layer. Kf values are calculated 

values that indicate the erodibility of the fine-earth 

fraction, or the material less than 2 millimeters in 

size. They are used in the Revised Universal Soil 

Loss Equation2 (RUSLE2). Kw estimates indicate 

the erodibility of the whole soil, including the rock 

fragments. Kw criteria are used in the determination of 

important farmland, including prime farmland.

Erosion factor (T)

The T factor is the soil loss tolerance used in the 

RUSLE2. It is defined as an estimated maximum rate 

of annual soil erosion that will permit crop productivity 

to be sustained economically and indefinitely. The 

five classes of T factors range from 1 ton per acre 

per year for very shallow soil to 5 tons per acre per 

year for very deep soil, which can more easily sustain 

productivity than shallower soils.

Flooding

Inundation by overflowing streams (fig. 20) or 

runoff from nearby slopes may damage crops or delay 

their planting and harvesting. Scouring can remove 

favorable soil material. Deposition of soil material can 

be beneficial or detrimental. Soil stratification (fig. 16) 

is an indication of deposition by flooding. Long periods 

of flooding reduce crop yields. Table 2 gives the 

frequency and duration classes used in soil surveys.

Table 2.—Flooding frequency and duration classes

Flooding frequency classes

None: Near 0 percent chance in any year, or less 

than 1 time in 500 years

Very rare: Less than 1 time in 100 years but more

than 1 time in 500 years

Rare: Nearly 1 time to 5 times in 100 years

Occasional: 5 to 50 times in 100 years

Frequent: More than 50 times in 100 years but 

less than a 50 percent chance in all months of 

any year

Very frequent: More than a 50 percent chance in

all months of any year

Flooding duration classes

Extremely brief: 0.1 hour to 4.0 hours

Very brief: 4 to 48 hours

Brief: 2 to 7 days

Long: 7 days to 30 days

Very long: 30 days

Onsite investigation may indicate that a map unit 

described as subject to flooding has areas that are 

now protected against flooding. 

Potential for frost action

Potential for frost action is the likelihood of upward 

or lateral movement of soil through the formation of 

ice lenses. Estimates are made from soil temperature, 

particle size, and soil water states. Frost can break 

compact and clayey layers into more granular forms. 

It can also break large clay aggregates into smaller 

aggregates that are more easily transported by 

water and wind. Frost heaving can harm improperly 

designed conservation structures and can destroy 

taprooted perennial crops.

High water table

A seasonal high water table is the highest average 

depth of free water during the wettest season. The 

ground water level, or water table, may be high year 

round or just during periods of heavy rainfall. How 

high the water table rises and how long it stays at that 

height affect the use of the soil. A perched water table 

usually occurs in areas where a hardpan, claypan, or 

other dense layer retards deeper water penetration. A 

water table that rises above the surface is considered 

ponding. 

Organic matter

The content of organic matter is estimated for 

each soil layer. A content of 1 percent organic 

matter is equivalent to 0.6 percent organic carbon. 

Organic matter promotes granulation, good tilth, 

and water infiltration; increases porosity; lowers 

bulk density; reduces plasticity and cohesion; and 

increases the available water capacity. It has a high 

cation-adsorption capacity, and it releases nitrogen, 

phosphorus, and sulfur as it decomposes.
16

Permeability

Permeability refers to the ability of soil to transmit 

water or air. In soil surveys, the term “permeability” 

indicates saturated hydraulic conductivity, which is 

influenced by texture, structure, bulk density, and 

large pores. Soil structure influences the rate of water 

movement through saturated soil, in part, by the size 

and shape of pores. Granular structure readily permits 

downward water movement, whereas platy structure 

requires water to flow more slowly over a much 

longer path (fig. 21). Permeability affects drainage 

design, irrigation scheduling, and many conservation 

practices. Permeability classes are shown in table 3.

Table 3.—Permeability classes

Class Rate (in/hr)

Impermeable...................................................<0.0015

Very slow ..................................................0.0015-0.06

Slow................................................................0.06-0.2

Moderately slow................................................0.2-0.6

Moderate ..........................................................0.6-2.0

Moderately rapid...............................................2.0-6.0

Rapid .................................................................6.0-20

Very rapid ..............................................................>20

Figure 20.—Flooding along the Missouri River.

Reaction

Soil pH is an expression of the degree of acidity or 

alkalinity of a soil. It influences the availability of plant 

nutrients. Compared to a neutral soil (pH 7.0), a very 

acid soil (pH less than 5.0) typically has lower levels 

of nitrogen, phosphorus, calcium, and magnesium 

available for plants and higher levels of available 

aluminum, iron, and boron. At the other extreme, 

if the pH is too high, the levels of available iron, 

manganese, copper, zinc, and especially phosphorus 

and boron may be low. A pH above 8.3 may indicate a 

significant level of exchangeable sodium.

Rock fragments

The size and percentage of rock fragments in the 

soil are important to land use. Rock fragments reduce 

the amount of water available to plants and may 

restrict some tillage operations. Particles larger than 

2 millimeters in diameter are called rock fragments. 

Those 2 millimeters to 3 inches in diameter are called 

pebbles or gravel; those 3 to 10 inches in diameter 

are called cobbles; and those more than 10 inches in 

diameter are called stones or boulders.
17

Root-restrictive layers

Some soils have layers that roots and water cannot 

easily penetrate. Physical root restriction may be 

expected in hard or soft bedrock (fig. 11) and in some 

soil layers, such as a fragipan or cemented hardpan. 

Intensive management may be required to reduce the 

effects of a poor rooting depth, a high water table, and 

a lower available water capacity.

Ripping a cemented pan or some other restrictive 

layers allows deeper root and water penetration. 

The physical root restrictions in many other layers, 

however, generally cannot be alleviated. For example, 

a change from a favorable particle size to sand, 

gravel, cobbles, stones, or boulders may indicate a 

zone of root restriction that cannot be alleviated.

If the soil layer is massive or has a weak or platy 

structure, resistance to root penetration generally is 

high for the combinations of texture and bulk density 

shown in table 4.

Salinity

Salts, mainly sodium, magnesium, calcium, and 

chloride or sulfate, may interfere with the absorption 

of water by plants. They also create a nutrient 

imbalance in some plants. Soils in which the electrical 

conductivity in the soil solution is greater than 2 

mmhos/cm are considered saline (fig. 16).

Figure 21.—Water movement through granular, prismatic, subangular blocky, and platy soils, respectively.

Sodium adsorption ratio (SAR)

SAR is a measure of the activities of sodium 

relative to calcium and magnesium in the soil solution. 

In soil that has an SAR value as low as 6 and has low 

salinity, dispersion of clay may be increased, resulting 

Table 4.—Bulk density/root-restriction in most soils

 Average

 Texture bulk density

Coarse sand, sand, loamy coarse 

sand, loamy sand, fine sand, and 

loamy fine sand..............................................>1.85

Very fine sand, loamy very fine sand,

fine sandy loam, coarse sandy loam,

very fine sandy loam, sandy loam, loam

that has an average of <18 percent clay .........>1.8

Loam, sandy clay loam, clay loam that

has an average of 18 to 35 percent clay ..........>1.7

Silt, silt loam, silty clay loam that has an

average of <35 percent clay ............................>1.6

Clay loam, sandy clay, clay, silty clay loam,

silty clay that has an average of 35 to 59

percent clay (>30 percent in Vertisols).............>1.5

Clay that has an average of >60 percent clay,

except in Vertisols ..........................................>1.35
18

in reduced aeration and permeability and increased 

susceptibility to erosion. Higher values may indicate 

surface conditions that take on a puddled appearance. 

Amendments, such as gypsum (CaSO4), along with 

irrigation and drainage can improve the unfavorable 

soil condition in many areas.

Slope

Slope is the gradient of an elevation change. A 

rise of 10 feet in a horizontal distance of 100 feet is 

a slope of 10 percent. Ranges of slope assigned to 

map units represent practical breaks on the landscape 

that are important for the use and management of 

the survey area (fig. 22). Terraces, irrigation, and 

tillage practices are all considered. For example, 

terraces can help to control erosion in some areas 

where slope is more than about 1 or 2 percent; 

thus, a separation of 0 to 2 percent and more than 

2 percent for the same kind of soil may be used in 

mapping. Slope classes are not site specific, however, 

and for conservation planning, onsite investigation is 

necessary to determine the slope.

Soil texture (USDA)

Texture is determined according to the relative 

proportions of sand, silt, and clay in the soil (fig. 23). 

Figure 24 illustrates the relative sizes of the three 

major soil particles.

Sandy soils tend to be characterized by low 

strength and a greater susceptibility to wind erosion 

and less water available to plants than soils of other 

textures. In addition, trenches and banks are highly 

susceptible to caving, which may pose a safety 

hazard. Water may pipe through terraces and other 

water impoundments.

Clayey soils generally have more available water 

than sandy soils. Loamy very fine sands and loamy 

fine sands, however, can hold moderate amounts 

of available water. Generally, the cation-exchange 

capacity increases with increases in content of clay 

and organic matter. Soils that have large amounts of 

clay fix more phosphorus than soils that have less 

clay. The type of clay also affects phosphorus fixation. 

Clayey soils that are high in content of montmorillonite 

tend to have the greatest capacity to shrink and swell 

(figs. 7 and 25). They retain large quantities of water, 

which affect tillage practices and can contribute to soil 

creep or landslides in sloping areas. Montmorillonitic 

Figure 22.—Slope classes.

Figure 23.—USDA soil texture classes.

Figure 24.—The relative sizes of sand, silt, and clay.
19

or other smectitic clays also have strong adhesive 

properties that bond particles together.

Silty soils have a higher available water capacity 

than sandy soils. In the absence of clay particles, silty 

soils have lower adhesive properties. Piping through 

terraces, levees, and pond embankments can be a 

problem. Trenches may cave, particularly in saturated 

soils.

In organic soils the term “muck” or “peat” is used 

in place of textural class names (fig. 4). Muck is 

well decomposed organic soil, and peat is raw, 

undecomposed material. The word “mucky” is used as 

an adjective to modify a texture class. An example is 

“mucky loam.” 

Adjectives describing rock fragments also are used 

to modify a texture. For example, some Hambright 

soils (fig. 11) have very cobbly layers.

Subsidence

Organic soils often subside when drained because 

of shrinkage from drying; loss of ground water, which 

physically floats the organic material; soil compaction; 

and oxidation of the material. Subsidence creates an 

uneven surface. Periodic surface smoothing or grading 

may be needed to maintain adequate irrigation 

systems. Draining and oxidation of the organic 

Figure 25.—Deep, wide cracks are common during dry periods 

in Vertisols. Maxwell soil. Typic Haploxerert. California.

material contribute large amounts of carbon to the 

atmosphere.

Some mineral soils subside because of lowering of 

ground water tables; removal of zones of soluble salts, 

such as gypsum and calcium carbonate, through 

leaching; and melting of ice lenses in frozen soils.

Wind erodibility group (WEG) and wind erodibility 

index (I)

WEG is a general grouping of soils with similar 

properties affecting their resistance to soil blowing. 

Soil texture, size of soil aggregates, presence of 

carbonates, and the degree of decomposition in 

organic soils are the major criteria used in grouping 

the soils. The groups are numbered 1 through 8. The 

number 1 represents sandy soils, which are the most 

susceptible to wind erosion (fig. 26), and the number 

8 represents gravelly or wet soils that are not subject 

to soil blowing. The wind erodibility index (I) is an 

estimate of soil loss in tons per acre per year. It is one 

of the criteria used in the determination of important 

farmland, including prime farmland.

Figure 26.—Evidence of erosion on a sandy soil partially 

protected by surface gravel.
20

Section 5: Management interpretations

Soil surveys commonly identify the more

 important soil characteristics that determine

 the soil-related limitations that affect 

farming. Interpretations for farming include soil 

productivity, placement of the soil in management 

groups, and presentation and evaluation of a number 

of soil properties affecting use. The interpretations 

are designed to warn of possible soil-related hazards 

in an area. Table 5 displays important soil property 

information related to agronomic interpretations. The 

following paragraphs describe some of the major 

agricultural interpretations.

Soil productivity

Productivity of the soil is the output or yield per 

acre of a specified crop or pasture species under 

a defined set of management practices. If the land 

is irrigated, yields are provided for irrigated and 

nonirrigated conditions. Management practices are 

usually defined for each class.

A “high” level of management provides necessary 

drainage, erosion control, protection from flooding, 

proper planting rates, suitable high-yielding varieties, 

appropriate and timely tillage, and control of weeds, 

plant diseases, and harmful insects. This management 

also includes favorable pH and optimal levels of plant 

nutrients; appropriate use of crop residue, manure, 

and green manure crops; and harvesting methods that 

ensure the smallest possible loss. For irrigated crops, 

the irrigation system is adapted to the soil and crops 

and good-quality irrigation water is uniformly applied 

as needed.

Irrigation

For most crops, the most favorable soils for 

irrigation are deep, nearly level, and well drained. 

They are characterized by good surface permeability 

and a high available water capacity. Irrigation water 

or rainwater can perch on a tillage pan, reducing the 

amount of oxygen in the root zone and increasing the 

amount of nitrogen lost to the atmosphere. 

Important considerations affecting the design of 

irrigation systems are feasible water application rates, 

ease of land leveling, drainage if necessary and its 

effect on the soil, the hazard of erosion, equipment 

limitations caused by steep slopes or rock fragments, 

and flooding.

Slope affects the performance of an irrigation 

system. Flood or furrow irrigation is used mainly on 

soils having slopes of less than 3 percent. Wheel lines 

and center pivots work well on slopes of as much as 

7 percent but with increasing difficulty. Drip systems 

work well even on steep slopes.

Most irrigated crops grow well if the rooting depth 

exceeds about 40 inches. A shallower root zone has a 

lower amount of available water, thus requiring more 

care in crop management and irrigation. Shallow 

soils, sandy soils, and soils that have rock fragments 

require more frequent irrigation than deep and finer 

textured soils. Frequent, light irrigation on fine textured 

soils helps to prevent cracking and thus reduces the 

amount of water lost through evaporation (fig. 25).

Chemical characteristics can be important. Salinity 

is particularly a problem where drainage conditions 

are unfavorable for the removal of soluble salts by 

flushing. Where only small differences in slope and 

elevation occur, salt-laden water can increase salinity 

and alkalinity in low areas (fig. 17).

Drainage

Drainage is the removal of excess water from 

soil. Determination of which soils meet the definition 

of “hydric soil” and “wetland” is needed to prevent 

draining of wetlands.

Soils that have intermediate saturated hydraulic 

conductivity (permeability) respond well to subsurface 

drains, open ditches, or a combination of these. 

In areas that have large amounts of excess water, 

drainage can be improved by smoothing or shaping 

the surface of the soil, provided that traffic-induced 

surface compaction is remedied. Smoothing or 

shaping increases runoff and reduces the amount of 

water to be disposed of by internal water movement. 

Stoniness, slope, silty soil low in content of clay, 

and physical soil barriers affect the installation and 

functioning of the drainage system. Caution is needed 

in areas of unstable soils. Silty soil material low in 

content of clay tends to move into and clog subsurface 

drains that are not adequately protected by filters. 

Coarse textured soils are unstable and may be 

droughty after drainage. Some wet soils have sulfides 

that oxidize on exposure to air, causing extreme 

acidity after drainage. Drainage water high in reduced 
21

iron may precipitate a “slime” that plugs drainage 

lines. Wet organic soils subside after drainage.

The effective rooting depth is an indicator of the 

depth to which soils can be drained. In deep soils 

without root-restrictive layers, depth is not a limitation. 

If a massive clayey layer or other root-restrictive layer 

occurs in the soil, effective drainage is more difficult. 

If drainage is impaired by a restrictive layer, trenching 

and installation of drain tiles are needed.

Erosion-control practices

The need for erosion control depends on the 

hazard of erosion and the cultivars grown. Some 

crops, such as hay and pasture, protect against 

erosion. For others, such as row crops, specific 

management practices are needed. The practices 

to be used should be selected only after onsite 

inspection. In some areas adequate erosion control 

can be achieved by simple application of one of 

the general practices. In other areas two or three 

different practices may be needed. In addition to cover 

crops, stripcropping, conservation tillage, terraces, 

diversions, and grassed waterways, other measures 

may be appropriate.

Other management interpretations

Some soil surveys, or addenda to the surveys, 

have special tables on important agronomic soil 

interpretations. A few tables show the potential of soils 

for a specified use, such as the potential for cropland. 

Table 5 identifies soil properties that influence 

agronomic uses.

Soil properties

Agronomic

use

Organic 

matter

Flooding Texture Bedrock 

or pan

pH SubsidenceCationexchange 

capacity

CaCO3 Slope Bulk

density

PermeabilityPotential 

for frost 

action

Available 

water 

capacity

Salinity/

alkalinity

Water 

table

Wind 

erodibility 

group

Erosion 

factors K 

and T

Tillage 

suitability • • • • • • • • Plant 

adaptability • • • • • • • • • • • • • •

Erodibility:

Wind

Water • • • • • • • • •

Irrigation

• • • • • • • • • • • • • •

Drainage

• • • • • • • • •

Crop yield 

productivity • • • • • • • • • • • • •

Conservation 

practices • • • • • • • • • • • • • • • • Land use 

capability • • • • • • • • • • • •

A bullet (•) indicates that the soil property affects the selected agronomic use.

Table 5.—Soil survey information that influences agronomic uses
22

Some tables group soils for specific programs, such 

as hydric soils, highly erodible lands, land capability 

classification, and prime or unique farmland.

Hydric soils formed under conditions of saturation, 

flooding, or ponding long enough during the growing 

season to develop anaerobic conditions (lack of 

oxygen) in the upper part (6 to 10 inches). The 

presence of hydric soils is one of three parameters 

needed for a site to be considered a wetland for 

Federal wetland protection programs and legislation. 

The presence of hydric soils can also be used to 

identify areas suitable for wetland restoration. Soil 

features that occur because of anaerobic conditions 

are used to confirm that a soil is hydric.

The national hydric soils list identifies map units 

that have components of hydric soils. A copy of the 

official hydric soils list can be downloaded from the 

following Web site: http://soils.usda.gov/use/hydric/. 

An interpretive map based on the hydric soils list 

can be created for an area of interest (AOI) in Web 

Soil Survey. After creating an AOI, click on the Soil 

Map tab. From the Soil Data Explorer tab, click on 

Suitabilities and Limitations for Use. Open Land 

Classifications, and select Hydric Rating by Map Unit.

Highly erodible soil and potentially highly erodible 

soil are listed in Section II of the NRCS Field Office 

Technical Guide. The criteria used to group highly 

erodible soils were formulated using the Universal 

Soil Loss Equation and the wind erosion equation. 

The criteria are in the National Food Security Act 

Manual. Soil use, including tillage practices, is not a 

consideration.

Areas defined as highly erodible can be held to 

an acceptable level of erosion by following approved 

practices in a conservation plan. Various conservation 

practices, such as crop residue management, 

reseeding to grasses, contour farming, and terraces, 

are used in conservation planning to reduce soil loss, 

maintain productivity, and improve water quality.

Land capability classes and, in most cases, 

subclasses are assigned to each soil. They 

suggest the suitability of the soil for field crops or 

pasture and provide a general indication of the 

need for conservation treatment and management. 

Capability classes are designated by either Arabic 

or Roman numerals (I through VIII), which represent 

progressively greater limitations and narrower choices 

for practical land use (fig. 27). 

Capability subclasses are soil groups within one 

class. They are designated by adding a small letter, 

e, w, s, or c, to the class numeral, for example, 

IIe. The letter e shows that the main hazard is the 

risk of erosion unless close-growing plant cover 

is maintained; w shows that water in or on the soil 

interferes with plant growth or cultivation (in some 

soils the wetness can be partly corrected by artificial 

drainage); s shows that the soil is limited mainly 

because it is shallow, droughty, stony, saline, or sodic; 

and c, used in only some parts of the United States, 

shows that the chief limitation is climate that is very 

cold or very dry.

In class I there are no subclasses because the 

soils of this class have few limitations. 

Prime farmland and other important farmland 

are identified by map unit name in the table “Prime 

Farmland and Other Important Farmlands” in Web 

Soil Survey. Prime farmland is land that has the 

best combination of climatic, physical, and chemical 

characteristics and landscape features for producing 

food, feed, forage, fiber, and oilseed crops. 

Unique farmland is land other than prime farmland 

that has the soil and climate characteristics needed 

for the production of specific high-value crops, such 

as citrus, tree nuts, olives, cranberries, fruit, and 

vegetables. Nearness to markets is needed. 

Farmlands of statewide and local importance are 

used for the production of food, feed, fiber, forage, and 

oilseed crops. They do not meet the criteria for prime 

farmland or unique farmland.

Figure 27.—Landscape with land capability classes outlined.
23

Section 6: General soil information

A general soil map is included in hard copies

 of most traditional soil surveys but is not

 available in Web Soil Survey. Different 

colors on this map show associations (or groupings) 

of the major soils in the survey area. Soils within an 

association may vary greatly in slope, depth, drainage, 

and other characteristics that affect management. 

Descriptions of the associations are included in a 

section called “General Soil Map Units.” 

The general soil map can be used to compare 

the suitability of large areas for general land uses. 

Because of the scale, it is not intended to be used to 

make management decisions on specific sites. Each 

color-coded area on the map has a corresponding 

description. For example, on the general soil map of 

Gentry County, Missouri, on page 24, areas coded 1 

and shaded light yellow designate the Lamoni-Shelby 

association. As the name of the association implies, 

Lamoni and Shelby soils are the major soils in this 

association. 

Some soil surveys include block drawings depicting 

the relationships of soils, parent material, and 

landscape positions. Figure 28 illustrates the dominant 

Lamoni and Shelby soils and the minor Sharpsburg, 

Grundy, and Colo soils as they occur in association 

1 in Gentry County. Note the relationships of parent 

material and landscape positions to the different 

soils. Refer to section 2 (“How is soil formed?”), 

including figure 12, for additional insights into these 

relationships.

Figure 28.—Relationship of soils, topography, and parent material in the Lamoni-Shelby association in Gentry County, Missouri.
24

Each area outlined on this map consists of more than one kind of soil. The map is thus meant for general 

planning rather than a basis for decisions on the use of specific tracts.
25

Legend

LAMONI-SHELBY association: Deep, moderately sloping

to moderately steep, somewhat poorly drained and moderately 

well drained soils that formed in glacial till; on uplands

NODAWAY-ZOOK association: Deep, nearly level, moderately 

well drained and poorly drained soils that formed in alluvium; 

on flood plains

GRUNDY association: Deep, gently sloping and moderately 

sloping, somewhat poorly drained soils that formed in loess; 

on uplands

GARA-ARMSTRONG-VANMETER association: Deep and 

moderately deep, moderately sloping to very steep, moderately 

well drained and somewhat poorly drained soils that formed in 

glacial till or residuum of shale; on uplands

Compiled 1983

U.S. Department of Agriculture

Natural Resources Conservation Service

Missouri Agricultural Experiment Station

GENERAL SOIL MAP

GENTRY COUNTY

MISSOURI

General Soil Map
26

Section 7: Detailed soil information

The Web Soil Survey (WSS) at http://

 websoilsurvey.nrcs.usda.gov/app/ provides

 the public with access to the most current 

official soil survey information. This Web application 

accesses the national SSURGO data in the Soil 

Data Mart. WSS users can outline their local area 

of interest (AOI) within a survey area or can select 

the whole soil survey area as the area of interest. 

If necessary, the AOI can cross traditional soil 

survey area boundaries. Various navigation tools are 

available to help the users navigate to the general 

area of their AOI. WSS also allows the users to 

import an AOI boundary from their local Geographic 

Information System (GIS). Recent aerial photography 

is used as the background for displaying the soil 

survey data in WSS.

After selecting an AOI, the user has the option 

of viewing the soil map and list of map units for the 

AOI. The list includes the acreage and percent of the 

AOI for each map unit. The user has the option to 

display either the traditional local map unit symbol or 

a nationally unique map unit symbol on the maps and 

in generated reports.

A description of each map unit is available in WSS. 

Areas delineated on the soil maps are not necessarily 

made up of just one type of soil but generally 

include smaller areas of contrasting soil types. The 

composition of each map unit is shown in the map unit 

description.

Thematic maps can be displayed for a variety 

of soil properties and interpretive ratings for the 

delineated soils. Maps of interpretive ratings display 

the limitations or suitability of each map unit for 

a particular land use. For each map displayed, a 

summary table showing the results is generated. The 

underlying SSURGO data can be downloaded for the 

defined AOI in standard format.

Standard tabular soil reports also can be generated 

for the AOI. These reports look much like the tables 

that have been included in the traditional hard copy 

soil survey publications.

The various maps and tabular reports that the user 

selects can be printed individually or compiled into 

a Custom Soil Resource Report via the Shopping 

Cart option. The output reports are compiled into a 

standard PDF file for download to the user’s local 

computer. The maps can be printed at various scales 

and on various sizes of paper, depending on what 

printer options the user has locally. Larger AOIs can 

be tiled to multiple pages for printing. This capability 

allows users to get just the content that they want or 

need to answer their particular resource management 

questions. 

Soil surveys provide sufficient information for 

the development of resource plans, but onsite 

investigation is needed to plan intensive uses of small 

areas. Some useful information that is not included 

in WSS is available in Section II of the NRCS Field 

Office Technical Guide (FOTG). The electronic version 

of the FOTG can be accessed at http://www.nrcs.

usda.gov/technical/efotg/.
27

Included are a variety of national interpretations 

as well as various state-specific interpretations. Not 

all interpretations are included for all areas of the 

nation. Some may not be applicable to all areas. Also, 

not all soil properties are populated for all areas. 

For example, information about salinity likely is not 

included for an area where salinity is not an issue.

Generated ratings that can be displayed as 

thematic maps in WSS are organized in a series of 

folders on the Suitabilities and Limitations tab. 

Specific soil properties or interpretations are

 sometimes difficult to locate within the Web

 Soil Survey (WSS) application. To assist the 

user, WSS includes a search function that allows the 

user to type in a soil property name or keyword. The 

tool returns a series of links that the user can click 

on to go directly to the desired information. The links 

may include general descriptive information, thematic 

maps, or tabular reports, as shown in the following 

image.

Section 8: Location of soil properties and interpretations

Location of Information

Section 8 describes where soil information can be found.
28

The Soil Properties and Qualities tab has a similar 

arrangement of folders and individual themes that 

allows the user to generate a thematic map of an 

individual soil property or quality.

Each folder has one or more interpretive ratings, as 

shown for Building Site Development in the following 

image.
29

The Soil Reports tab is organized in a similar fashion. These reports are tabular soil 

reports with formats similar to those that have traditionally been included in published 

hard copy soil surveys.
30

References

Andrew R. Aandahl. 1982. Soils of the Great Plains. University of Nebraska Press. 

Huddleston, J. Herbert, and Gerald F. King. 1984. Manual for Judging Oregon Soils. 

Oregon State University Extension Service, Extension Manual 6.

Scrivner, C.L., and J.C. Baker. 1975. Evaluating Missouri Soils. Circular 915, Extension 

Division, University of Missouri-Columbia.

Smith, C.W. 1989. The Fertility Capability Classification System (FCC): A Technical 

Classification System Relating Pedon Characterization Data to Inherent Fertility 

Characteristics. Doctoral Thesis. Department of Soil Science, North Carolina State 

University, Raleigh, North Carolina.

Soil Survey Division Staff. 1993. Soil Survey Manual. Soil Conservation Service. U.S. 

Department of Agriculture Handbook 18. Available online (http://soils.usda.gov/

technical/manual/).

United States Department of Agriculture, Natural Resources Conservation Service. 

National Soil Survey Handbook, title 430-VI. Available online (http://soils.usda.

gov/technical/handbook/). Accessed 1/20/2010.

United States Department of Agriculture. 1988. From the Ground Down: An 

Introduction to Soil Surveys. Soil Conservation Service. Columbia, Missouri.