Chapter Soil and Soil Survey

1

By Soil Science Division Staff. Revised by Craig Ditzler and 

Larry West, USDA-NRCS.

This chapter describes the term “soil survey” within the context 

of the National Cooperative Soil Survey (NCSS) in the United 

States. It discusses the development of pedology and the important 

concept of soils as natural three-dimensional bodies that form as a result 

of the interaction of five soil-forming factors. The repeating patterns 

formed by these natural bodies of soil in the landscape allow soil 

scientists to develop predictive soil-landscape models, which serve as 

the scientific foundation for making soil surveys. Important milestones 

in the development of the Soil Survey in the United States are discussed 

at the end of this chapter. 

Soil Survey—Definition and Description

A soil survey describes the characteristics of the soils in a given area, 

classifies the soils according to a standard system of taxonomy, plots 

the boundaries of the soils on a map, stores soil property information in 

an organized database, and makes predictions about the suitability and 

limitations of each soil for multiple uses as well as their likely response 

to management systems. The information collected in a soil survey helps 

in the development of land use plans and can be used to evaluate and 

predict the effects of land use on the environment.

A soil map consists of many individual delineations showing the 

location and extent of different soils. The collection of all delineations 

that have the same symbol on the map (e.g., 34B) are a “map unit.” Each 

map unit is named for one or more soils or nonsoil areas (e.g., Sharpsburg 

silt loam). Each kind of soil or nonsoil (e.g., Rock outcrop) making up 

the composition of a map unit is a map unit component. See chapter 4 for 

a full discussion of map units and their components. 
2 Chapter 

The soils are natural three-dimensional bodies occupying a 

characteristic part of the landscape. Soil survey maps are therefore 

different from other maps that show just one or a few specific soil 

properties or other environmental information. The concept of soil survey 

as defined for the NCSS is related to, but does not include, maps showing 

the distribution of a single soil property (such as texture, slope, or depth) 

alone or in limited combinations; maps showing the distribution of soil 

qualities (such as productivity or erodibility); and maps of soil-forming 

factors (such as climate, topography, vegetation, or geologic material). 

A soil map from a soil survey, as defined here, delineates areas occupied 

by different kinds of soil, each of which has a unique set of interrelated 

properties characteristic of the material from which it formed, its 

environment, and its pedogenic history. The soils mapped by the NCSS 

are identified by names that serve as references to a national system of 

soil classification.

The geographic distribution of many individual soil properties or soil 

qualities can be extracted from soil maps and shown on separate maps for 

special purposes, such as showing predicted soil behavior for a particular 

use. Numerous interpretative maps can be derived from a soil map, and 

each of these maps would differ from the others according to its purpose. 

A map made for one specific interpretation rarely can serve a different 

purpose.

Maps that show one or more soil properties can be made directly 

from field observations without making a basic soil map. Such maps 

serve their specific purposes but have few other applications. Predictions 

of soil behavior can also be mapped directly; however, most of these 

interpretations will need to be changed with changes in land use and in 

the cultural and economic environment. For example, a map showing the 

productivity of crops on soils that are wet and undrained has little value 

after drainage systems have been installed. If the basic soil map is made 

accurately, and a wide array of soil property data is collected and stored 

in an organized database, interpretative maps can be revised as needed 

without additional fieldwork. In planning soil surveys, this point needs 

to be emphasized. In some cases, inventories are made for some narrow 

objective, perhaps at a cost lower than that of a soil survey. Generally, 

maps for these inventories quickly become obsolete. They cannot be 

revised without fieldwork because vital data are missing, facts are mixed 

with interpretations, or boundaries between significantly different soil 

units have been omitted.

The basic objective of soil surveys is the same for all kinds of land, 

but the number of map units, their composition, and the detail of mapping 

vary with the complexity of the soil patterns and the specific needs 
Soil Survey Manual

of the users. Thus, a soil survey is designed for the soils and the soilrelated problems of the area. Soil surveys increase general knowledge 

about soils and serve practical purposes. They provide soil information 

about specific geographic areas needed for regional or local land use 

plans. These plans include resource conservation for farms and ranches, 

development of reclamation projects, forest management, engineering 

projects, as well as other purposes.

Early Concepts of Soil

One of the earliest scholars of soils in the United States was Edmund 

Ruffin of Virginia. He worked diligently to find the secret of liming and 

discovered what is now called exchangeable calcium. After writing a brief 

essay in the American Farmer in 1822, he published the first edition of 

An Essay on Calcareous Manures in 1832. Much of what Ruffin learned 

about soils had to be rediscovered because his writings were circulated 

only in the South.

E.W. Hilgard was one of the first modern pedologists in the United 

States. His early concepts of soil (Hilgard, 1860, 1884, 1906) were 

based on ideas developed by the German chemist Justus von Liebig 

and modified and refined by agricultural scientists who worked on soil 

samples in laboratories, in greenhouses, and on small field plots. Soils 

were rarely examined below the depth of normal tillage. The chemists 

had a “balance-sheet” theory of plant nutrition. Soil was considered a 

more or less static storage bin for plant nutrients—the soils could be 

used and replaced. This concept still has value when applied within the 

framework of modern soil science, although a useful understanding of 

soils goes beyond the removal of nutrients from soil by harvested crops 

and their return to soil through manure, lime, and fertilizer.

Early geologists generally accepted the balance-sheet theory of soil 

fertility and applied it within the framework of their own discipline. They 

described soil as disintegrated rock of various sorts—granite, sandstone, 

glacial till, etc. However, they also described how the weathering 

processes modified this material and how geologic processes shaped it 

into landforms (such as glacial moraines, alluvial plains, loess plains, 

and marine terraces). N.S. Shaler’s monograph on the origin and nature 

of soils summarized the late 19th century geological concept of soils 

(Shaler, 1891). Other details were added by G.P. Merrill (1906).

Near the end of the 19th century, Professor Milton Whitney 

inaugurated the National Soil Survey Program (Jenny, 1961). In the 

newly organized soil research unit of the U.S. Department of Agriculture, 
4 Chapter 

Whitney and his coworkers discovered great variations among natural 

soils—persistent variations that were in no way related to the effects of 

agricultural use. They emphasized the importance of soil texture and the 

capacity of the soil to furnish plants with moisture as well as nutrients. 

About this time, Professor F.H. King of the University of Wisconsin also 

reported the importance of the physical properties of soils (King, 1910).

Early soil surveys were made to help farmers locate soils responsive 

to different management practices and to help them decide what crops 

and management practices were most suitable for the particular kinds 

of soil on their farms. Many who worked on these early surveys were 

geologists because only geologists were skilled in the field methods and 

scientific correlation needed for the study of soils. They thought of soils 

as mainly the weathering products of geologic formations, defined by 

landform and lithologic composition. Most of the soil surveys published 

before 1910 were strongly influenced by these concepts. Those published 

from 1910 to 1920 were further refined and recognized more soil features 

but retained fundamentally geological concepts.

Early field workers soon learned that many important soil properties 

were not necessarily related to either landform or kind of rock. They 

noted that soils with poor natural drainage had different properties than 

soils with good natural drainage and that many sloping soils were unlike 

level ones. Topography was clearly related to soil profile differences. 

Soil structure was described in soil survey as early as 1902, in the soil 

survey of the Dubuque Area, Iowa (Fippin, 1902). The 1904 soil survey 

of Tama County, Iowa (Ely et. al., 1904) reported that soils that had 

formed under forest contrasted markedly with other soils that had similar 

parent material but formed under grass.

Soils as Natural Bodies

The balance-sheet theory of plant nutrition dominated laboratory 

work, while the geological concept dominated fieldwork. Both approaches 

were taught in many classrooms until the late 1920s. Although broader 

and more generally useful concepts of soil were being developed by some 

soil scientists, especially Hilgard (1860) and Coffey (1912) in the U.S. 

and soil scientists in Russia, the necessary data for formulating these 

broader concepts came from the fieldwork of the Soil Survey during the 

first decade of its operations in the United States. The concept of the solum 

and the A-B-C horizon nomenclature were becoming central to pedology 

and soil survey (Tandarich et al., 2002). After the work of Hilgard, the 

most significant advance toward a more satisfactory concept of soil was 

made by G.N. Coffey. Coffey determined that the ideal classification of 
Soil Survey Manual

soil was a hierarchical system based on the unique characteristics of soil 

as “a natural body having a definite genesis and distinct nature of its own 

and occupying an independent position in the formations constituting the 

surface of the earth” (Cline, 1977).

Beginning in 1870, the Russian school of soil science under the 

leadership of V.V. Dokuchaev and N.M. Sibertsev was developing a new 

concept of soil. The Russian scientists conceived of soils as independent 

natural bodies, each with unique properties resulting from a unique 

combination of climate, living matter, parent material, relief, and time 

(Gedroiz, 1925). They hypothesized that properties of each soil reflected 

the combined effects of the particular set of genetic factors responsible 

for the soil’s formation, emphasizing the importance of the “zonal” 

concept (i.e., the bioclimatic zone in which the soil formed). Hans Jenny 

later emphasized the functional relationships between soil properties and 

soil formation. The results of this work became generally available to 

Americans through the publication in 1914 of K.D. Glinka’s textbook 

in German and especially through its translation into English by C.F. 

Marbut in 1927 (Glinka, 1927).

The Russian concepts were revolutionary. Soil properties were no 

longer based wholly on inferences from the nature of rocks or from 

climate or other environmental factors, considered singly or collectively. 

Instead, the integrated expression of all these factors could be seen in the 

morphology of the soils. This concept required that all properties of soils 

be considered collectively in terms of a completely integrated natural 

body. In short, it made possible a science of soil.

As a result of the early enthusiasm for the new concept and for the 

rising new discipline of soil science, some suggested that the study of soil 

could proceed without regard to the older concepts derived from geology 

and agricultural chemistry. Certainly, the reverse was true. Besides laying 

the foundation for a soil science with its own principles, the new concept 

made the other sciences even more useful. Soil morphology provides a 

firm basis on which to group the results of observation, experiments, and 

practical experience and to develop integrated principles that predict the 

behavior of soils.

Under the leadership of C.F. Marbut, the Russian concept was 

broadened and adapted to conditions in the United States (Marbut, 1921). 

As mentioned earlier, this concept emphasized individual soil profiles and 

subordinated external soil features and surface geology. By emphasizing 

soil profiles, however, soil scientists initially tended to overlook the 

natural variability of soils, which can be significant even within a small 

area. Overlooking the variability of soils seriously reduced the value 

of maps that showed the location of soils. This weakness soon became 
6 Chapter 

evident in the U.S., perhaps because of the emphasis on making detailed 

soil maps for their practical, predictive value. Progress in transforming 

the profile concept into a more reliable predictive tool was rapid because 

a large body of important field data had already been accumulated. By 

1925, a large amount of morphological and chemical work was being 

done on soils throughout the country. The data collected by 1930 were 

summarized and interpreted in accordance with this concept, as viewed 

by Marbut in his work on the soils of the United States (Marbut, 1935).

Early emphasis on genetic soil profiles was so great as to suggest that 

material lacking a genetic profile, such as recent alluvium, was not soil. A 

sharp distinction was drawn between rock weathering and soil formation. 

Although a distinction between these sets of processes is useful for some 

purposes, rock and mineral weathering and soil formation commonly are 

indistinguishable.

The concept of soil was gradually broadened and extended during the 

years following 1930, essentially through consolidation and balance. The 

major emphasis had been on the soil profile. After 1930, morphological 

studies were extended from single pits to long trenches or a series of 

pits in an area of a soil. The morphology of a soil came to be described 

by ranges of properties deviating from a central concept instead of by a 

single “typical” profile. The development of techniques for mineralogical 

studies of clays also emphasized the need for laboratory studies.

The clarification and broadening of soil science also was due to 

the increasing emphasis on detailed soil mapping. Concepts changed 

with increased emphasis on predicting crop yields for each kind of soil 

shown on the maps. Many of the older descriptions of soils had not 

been quantitative enough and the units of classification had been too 

heterogeneous to use in making the yield and management predictions 

needed for planning the management of individual farms or fields.

During the 1930s, soil formation was explained in terms of loosely 

conceived processes, such as “podzolization,” “laterization,” and 

“calcification.” These were presumed to be unique processes responsible 

for the observed common properties of the soils of a region (Jenny, 1946).

In 1941, Hans Jenny’s Factors of Soil Formation: A System of 

Quantitative Pedology concisely summarized and illustrated many of the 

basic principles of modern soil science to that date (Jenny, 1941). Since 

1940, time has assumed much greater significance among the factors of 

soil formation and geomorphological studies have become important in 

determining the time that soil material at any place has been subjected 

to soil-forming processes. Meanwhile, advances in soil chemistry, soil 

physics, soil mineralogy, and soil biology, as well as in the basic sciences 

that underlie them, have added new tools and new dimensions to the 
Soil Survey Manual

study of soil formation. As a consequence, the formation of soil has come 

to be treated as the aggregate of many interrelated physical, chemical, 

and biological processes. These processes are subject to quantitative 

study in soil physics, soil chemistry, soil mineralogy, and soil biology. 

The focus also has shifted from the study of gross attributes of the whole 

soil to the co-varying detail of individual parts, including grain-to-grain 

relationships.

Early Development of Soil Classification

C.F. Marbut strongly emphasized that the classification of soils should 

be based on morphology instead of on theories of soil genesis, because 

theories are both ephemeral and dynamic. He perhaps overemphasized 

this point because some scientists assumed that soils had certain 

characteristics without ever actually examining them. Marbut stressed 

that examination of the soils themselves was essential in developing a 

system of soil classification and in making usable soil maps. However, 

Marbut’s work reveals his personal understanding of the contributions of 

geology to soil science. His soil classification of 1935 relied heavily on 

the concept of a “normal soil,” the product of equilibrium on a landscape 

where downward erosion keeps pace with soil formation. Continued work 

in soil classification by the U.S. Department of Agriculture culminated in 

the release of a new system published in the 1938 Yearbook of Agriculture 

in the chapter “Soil Classification” (Baldwin et al., 1938).

In both the early classification developed by Marbut and the later 

1938 classification developed by USDA, the classes were described 

mainly in qualitative terms. Because the central concept of each class 

was described but the limits between classes were not, some soils seemed 

to be members of more than one class. The classes were not defined in 

quantitative terms that would permit consistent application of the system 

by different scientists. Neither system definitely linked the classes 

of its higher categories, which were largely influenced by the genetic 

concepts initiated by the Russian soil scientists, to the soil series and 

their subdivisions that were used in soil mapping in the United States. 

Both systems reflected the concepts and theories of soil genesis of the 

time, which were themselves predominantly qualitative in character. 

Modification of the 1938 system in 1949 corrected some deficiencies 

but also illustrated the need for a reappraisal of concepts and principles. 

One continuing problem was that a scientist required knowledge about 

the genesis of the soil to classify it. This information was often lacking 

or was disagreed upon by soil surveyors. It was determined that a new 
8 Chapter 

classification system was required, one that could be applied consistently 

by an increasingly large and varied cadre of soil surveyors. 

Modern Concept of Soil

Soil as defined in Soil Taxonomy (Soil Survey Staff, 1999) is “a natural 

body comprised of solids (minerals and organic matter), liquid, and gases 

that occurs on the land surface, occupies space, and is characterized by 

one or both of the following: horizons, or layers, that are distinguishable 

from the initial material as a result of additions, losses, transfers, and 

transformations of energy and matter or the ability to support rooted 

plants in a natural environment.”

The “natural bodies” of this definition include all genetically related 

parts of the soil. A given part, such as a cemented layer, may not be 

capable of supporting plants. However, it is still a part of the soil if 

it is genetically related to the other parts and if the body as a unit is 

either capable of supporting plants or has horizons or layers that are the 

result of the pedogenic processes, i.e., additions, losses, transfers, and 

transformations (Simonson, 1959). Nearly all natural bodies recognized 

as “soil” are capable of supporting plants. Some that cannot support 

higher plants are still recognized as soil because they are affected by 

pedogenic development. Soils in very harsh environments, such as 

Antarctica, are an example. The definition of soil also includes natural 

bodies that are capable of supporting plants even though they do not have 

genetically differentiated parts. For example, a fresh deposit of alluvium 

or earthy constructed fill is soil if it can support plants. 

Bodies of water that support floating plants, such as algae, are 

not considered soil because these plants are not rooted. However, the 

sediment below shallow water is soil if it can support bottom-rooting 

plants (such as cattails, reeds, and seaweed) or if the sediment exhibits 

changes due to pedogenic processes. These soils are commonly referred 

to as “subaqueous soils” (see chapter 10). The above-ground parts of 

plants are also not soil, although they may support parasitic plants. Also 

excluded is rock that mainly supports lichens on the surface or plants 

only in widely spaced cracks.

The transition from nonsoil to soil can be illustrated by recent lava 

flows in warm regions under heavy and very frequent rainfall. In those 

climates, plants become established very quickly on the basaltic lava, 

even though there is very little earthy material. They are supported by the 

porous rock filled with water containing plant nutrients. The dominantly 

porous, broken lava in which plant roots grow is soil.
Soil Survey Manual

Marbut’s definition of soil as “the outer layer” of the Earth’s crust 

implied a concept of soil as a continuum (Marbut, 1935). The current 

definition refers to soil as a collection of natural bodies on the surface 

of the Earth. It divides Marbut’s continuum into discrete, defined parts 

that can be treated as members of a population. The perspective of soil 

has changed from one in which the whole was emphasized and its parts 

were loosely defined to one in which the parts are sharply defined and the 

whole is an organized collection of these parts.

Development of Soil Taxonomy

More than 15 years of work under the leadership of Dr. Guy Smith 

culminated in a new soil classification system. Categories and classes of 

the new taxonomy were direct consequences of new and revised concepts 

and theories. This system became the official classification system of the 

U.S. National Cooperative Soil Survey in 1965 and was published in 

1975 as Soil Taxonomy: A Basic System of Soil Classification for Making 

and Interpreting Soil Surveys (Soil Survey Staff, 1975). The system’s 

most significant contribution was the establishment of taxonomic class 

limits and their quantitative definitions, whereby an individual soil could 

belong to only one class. Soil genesis was no longer used directly in 

determining the correct classification. Instead, diagnostic horizons and 

features that are the morphological expression of major known genetic 

processes were defined and used. In this way the current understanding 

of soil genesis, while indirectly incorporated in the taxonomy, is one 

step removed from the process of classifying a soil (Smith, 1963). The 

application of quantitative diagnostic horizons and features as criteria 

to be used in soil classification has been widely adopted in other soil 

classification systems around the world, perhaps most notably by the 

World Reference Base (IUSS Working Group WRB, 2014), sponsored 

by the Food and Agriculture Organization of the United Nations. 

The system of soil classification discussed in Soil Taxonomy is 

dynamic and can change as new knowledge is obtained. The theories on 

which the system is based are tested every time the taxonomy is applied. 

During the 1980s and 1990s, nine international committees contributed 

to major revisions of the taxonomy. This work culminated in the printing 

of the second edition of Soil Taxonomy (Soil Survey Staff, 1999). In 

addition, many individual proposals for change have been incorporated 

in editions of the Keys to Soil Taxonomy, which have been published 

periodically since the first edition of Soil Taxonomy was published in 

1975. The work of a 10th international committee, which addressed the 
10 Chapter 

impact of human influences on soils, resulted in important changes. These 

changes are reflected in the 12th edition of the Keys to Soil Taxonomy

(Soil Survey Staff, 2014).

Scientific Foundation of Soil Survey

Soil survey is grounded in scientific principles that can be described 

by the factors of soil formation and by the relationships between 

landscapes, landforms, and soils. The soil-forming factors are responsible 

for the genetic development of soil profiles. The relationships between 

landscapes, landforms, and soils are used to understand the predicable 

patterns of natural soil bodies in the landscape.

Factors that Control the Distribution of Soils

The properties of soil vary from place to place, but this variation 

is not random. Natural soil bodies are the result of climate and living 

organisms acting on parent material, with topography or local relief 

exerting a modifying influence and with enough time for soil-forming 

processes to act. For the most part, soils are the same wherever all 

elements of the five factors are the same. Under similar environments in 

different places, soils are similar. This regularity permits prediction of 

the location of many different kinds of soil. This fundamental principle 

makes soil survey practical (Hudson, 1992).

When soils are studied in small areas, the effects of topography 

(or local relief), parent material, and time on soil become apparent. In 

humid regions, for example, wet soils and the properties associated with 

wetness are common in low-lying places while better drained soils are 

common in higher lying areas. The correct conclusion to draw from 

these relationships is that topography or relief is important. In arid 

regions, the differences associated with relief may be manifested in 

variations in salinity or sodicity, but the conclusion is the same. In a 

local environment, different soils are associated with contrasting parent 

materials, such as residuum from shale and residuum from sandstone. 

The correct conclusion to draw from this relationship is that parent 

material is important. Soils on a flood plain differ from soils on higher 

and older terraces where there is no longer deposition of parent material 

on the surface. The correct conclusion to draw from this relationship is 

that time is important. The influence of topography, parent material, and 

time on the formation of soil is observed repeatedly while studying the 

soils of an area.
Soil Survey Manual 

With the notable exception of the contrasting patterns of vegetation 

in transition zones, local differences in vegetation are closely associated 

with differences in relief, parent material, or time. The effects of 

microclimate on vegetation may be reflected in the soil, but such effects 

are likely associated with differences in local relief.

Regional climate and vegetation influence the soil as well as 

topography/relief, parent material, and time. In spite of local differences, 

most of the soils in an area typically have some properties in common, 

which reflect the soil-forming factors influencing the soils regionally. The 

low-base status of many soils in humid regions or regions with naturally 

acid rock or sediment stands in marked contrast to the typical high-base 

status in arid regions or regions with calcareous sandstone or limestone. 

In old landscapes of humid regions, however, low-base status is so 

commonplace that little significance is attached to it when considered 

only from the narrow perspective of old landscapes in a humid region 

alone. 

Regional patterns of climate, vegetation, and parent material can be 

used to predict the kinds of soil in large areas. The local patterns of 

topography/relief, parent material, and time, and their relationships to 

vegetation and microclimate, can be used to predict the kinds of soil 

in small areas. Soil surveyors learn to use local features, especially 

topography and associated vegetation, as indicators of unique combinations of all five soil-forming factors. These features are used to predict 

boundaries of different kinds of soil and to predict some of the properties 

of the soil within those boundaries.

Soil-Landscape Relationships

Geographic order suggests natural relationships. For example, 

weathering and erosion of bedrock by running water commonly sculpt 

landforms within a landscape. Over the ages, earthy material has been 

removed from some landforms and deposited on others. Landforms are 

interrelated. An entire area has unity through the interrelationships of its 

landforms. 

Each distinguishable landform may have one kind of soil or several. 

Climate, including its change over time, commonly will have been about 

the same throughout the extent of a minor landform. In addition, the 

kinds of vegetation associated with climate will likely have been fairly 

uniform. Relief varies within some limits that are characteristic of the 

landform. The time that the material has been subjected to soil formation 

will probably have been about the same throughout the landform. The 

surface of the landform may extend through one kind of parent material 
12 Chapter 

and into another. Of course, position on the landform may have influenced 

soil-water relationships, microclimate, and vegetation.

Just as different kinds of soil are commonly associated in a landscape, 

several landscapes are commonly associated in still larger areas. These 

areas cover thousands or tens of thousands of square kilometers. Many 

can be identified on photographs taken from satellites. From this vantage 

point, broad physiographic regions are apparent. Examples in the U.S. 

are the East Gulf Coastal Plain, the Appalachian Plateau, the Wyoming 

Basin, and the Great Plains. These broad units typically have some 

unity of landscape, as indicated by such terms as “plain,” “plateau,” and 

“mountain.” These physiographic units are composed of many kinds of 

soil.

The main relief features of a physiographic unit are commonly the 

joint products of deep-seated geologic forces and a complex set of surface 

processes that have acted over long spans of time. Within a physiographic 

unit, groups of minor landforms are shaped principally by climatecontrolled processes. The climate and biological factors, however, vary 

much less within a geomorphic unit than across a continent.

Still broader than the geomorphic units are great morphogenetic 

regions that have distinctive climates. For example, one classification recognizes glacial, periglacial, arid, semiarid-subhumid, humidtemperate, and humid-tropical climatic regions associated with distinctive 

sets of geomorphic processes. Other major regions are characterized 

by seasonal climatic variation. These geomorphic-climatic regions are 

related to soil moisture and soil temperature regimes. Thus, the great 

climatic regions are divided into major physiographic units. Landscapes 

and associated landforms are small parts of these units and are commonly 

of relatively recent origin.

The landforms important in soil mapping may include constructional 

units, such as glacial moraines and stream terraces, and elements of 

local sequences of graded erosional and constructional land surfaces. 

These bear the imprint of local, base-level controls under climateinduced processes. Most surfaces that have formed within the last 10,000 

years have been subject to climatic and base-level controls similar to 

those of the present. Older surfaces may retain the imprint of climatic 

conditions and related vegetation of the distant past. Most present-day 

landforms started to form during the Quaternary period; some started in 

the late Tertiary period. In many places, conditions of the past differed 

significantly from those of the present. Understanding climatic changes, 

both locally and worldwide, into the far past contributes to understanding 

the attributes of present-day landforms.
Soil Survey Manual 

Geomorphic processes are important in mapping soils. Soil scientists 

need a working knowledge of local geomorphic relationships in areas 

where they map. They should also understand the interpretations of 

landforms and land surfaces made by geomorphologists. The intricate 

interrelationships of soil and landscape are best studied by collaboration 

between soil scientists and geomorphologists. Standards and protocols 

for describing landscapes and geomorphology are discussed in chapter 2.

Development of the Soil Survey in the U.S.

Soil surveys were authorized in the United States by the U.S. 

Department of Agriculture Appropriations Act for fiscal year 1896, which 

provided funds for an investigation “of the relation of soils to climate and 

organic life” and “of the texture and composition of soils in field and 

laboratory.” In 1966, Congress expanded the scope of the Soil Survey 

Program and further clarified its intent in Public Law 89-560, the Soil 

Survey for Resource Planning and Development Act. This legislation

recognized that soil surveys are needed by States and other public 

agencies to support community planning and resource development 

in order to protect and improve the quality of the environment, meet 

recreational needs, conserve land and water resources, and control and 

reduce pollution from sediment and other pollutants in areas of rapidly 

changing uses.

Many soil surveys have been initiated, completed, and published 

cooperatively by the U.S. Department of Agriculture, State agencies, 

and other Federal agencies. The total effort is the National Cooperative 

Soil Survey (NCSS). The NCSS is a nationwide partnership of Federal, 

regional, State, and local agencies and private entities and institutions. 

This partnership works to cooperatively investigate, inventory, document, 

classify, interpret, disseminate, and publish information about soils of the 

United States and its trust territories and commonwealths.

The following discussion highlights some of the important developments that helped shape the U.S. soil survey over its more than 100-year 

history.

1896 to 1920

In 1899, the U.S. Department of Agriculture completed field 

investigations and soil mapping of portions of Utah, Colorado, New 

Mexico, and Connecticut. Reports of these soil surveys and similar 
14 Chapter 

works were published by legislative directive. At the same time, the State 

of Maryland, using similar procedures and State funds, completed a soil 

survey of Cecil County. 

The early soil surveys investigated the use of soils for farming, 

ranching, and forestry. Eventually, soil survey data began to be applied 

to other uses, such as highways, airfields, and residential and industrial 

developments. As more surveys were made and their use expanded, 

the knowledge about soils—their nature, occurrence, and behavior 

for defined uses and management—also increased. The Highway 

Department of Michigan was applying soil survey data and methods in 

planning highway construction in the late 1920s. At about the same time, 

soil surveys in North Dakota were being used in tax assessment.

1920 to 1950

Soil surveys published between 1920 and 1930 reveal a marked 

transition from earlier concepts that emphasized soil profiles and soils as 

independent bodies. The maps retained significant geologic boundaries as 

soil maps do today. Many of the surveys of that period provide excellent 

general maps for evaluating engineering properties of geologic material. 

In addition, maps and texts of the period show more recognition of other 

soil properties significant to farming and forestry than do earlier surveys 

and have value for broad generalizations about farming practices in large 

areas. To meet the needs of planning the management of individual fields 

and farms, greater precision of interpretation was required. The changing 

objectives of soil surveys initiated changes in methods and techniques 

that would make surveys more useful and forced scientists to reconsider 

the concept of soil itself.

Beginning in the 1930s, the Soil Conservation Service (SCS) 

emphasized the control of soil erosion as it used soil surveys for the 

resource conservation planning of farms and ranches. In the 1950s, soil 

survey information was used extensively in urban land development in 

Fairfax County, Virginia, and in the subdivision design of suburban areas 

of Chicago, Illinois. Soil surveys were an important base for resource 

information in regional land use planning in southeastern Wisconsin. 

Rural land zoning also relied on soil surveys. 

Several other advancements contributed to the expansion and 

increased precision of soil survey. An early change was the use of aerial 

photographs as base maps in detailed soil mapping during the late 

1930s and early 1940s. Aerial photos served not only as base maps that 

improved the surveyor’s ability to locate their positions in the field but 

also were used in stereo pairs to view the landscape in three dimensions. 
Soil Survey Manual 

The use of stereo pairs greatly enhanced the surveyor’s ability to place 

soil boundaries correctly in relation to position on the landform. 

Before 1950, the primary applications of soil surveys were 

farming, ranching, and forestry. Applications for highway planning 

were recognized in some States as early as the late 1920s, and soil 

interpretations were placed in field manuals for highway engineers of 

some States during the 1930s and 1940s. However, the changes in soil 

surveys during this period were mainly responses to the needs of farmers, 

ranchers, and forest managers. 

1950 to 1970

During the 1950s and 1960s, nonfarm uses of the soil increased 

rapidly. This created a great need for information about the effects of soils 

on these nonfarm uses. Beginning around 1950, cooperative research 

with the Bureau of Public Roads and with State highway departments 

established a firm basis for applying soil surveys to road construction. 

The laboratories of many State highway departments assisted soil survey 

operations by characterizing soils for properties such as particle-size 

distribution, plasticity index, and liquid limit in order to determine their 

proper placement in engineering classification systems. Soil scientists, 

engineers, and others worked together to develop interpretations of 

soils for roads and other nonfarm uses. These interpretations, which 

have become standard parts of published soil surveys, require different 

information about soils. Some soil properties that are not important 

for plant growth are very important for building sites, sewage disposal 

systems, highways, pipelines, and recreational development. Because 

many of these uses of soil require very large capital investments per unit 

area, errors can be extremely costly. Consequently, the location of soil 

boundaries, the identification of the delineated areas, and the quantitative 

definition of map units have assumed great importance.

In 1966, the Soil Survey for Resource Planning and Development 

Act recognized the expanding role of soil survey in supporting efforts 

to protect and improve the environment. It led to increased efforts to 

provide technical assistance in the use of soil survey information for land 

use planning, conservation, and development activities.

1970 to 2000

The use of aerial photography in soil survey was further enhanced by 

the introduction of orthophotography for the base map in publications. 

Aerial photographs contain inherent cartographic distortion and are 
16 Chapter 

therefore not true to scale across all parts of the image. Orthophotographs 

are digitally rectified to correct the spatial relationship of locations on 

the photo. Therefore, they provide a cartographically accurate base map 

to which field-drawn boundaries can be transferred. This advancement, 

coupled with advances in computer technology, soon led to the 

proliferation of digitized soil surveys throughout the 1990s and early 

2000s. These surveys became widely available for use in geographic 

information systems (GIS) and over the Internet. Combining soil survey 

data with other resource and cultural data layers in a GIS greatly enhanced 

the ways in which soil survey information could be used.

The adoption of Soil Taxonomy in 1975 as the official system for 

classifying soils in the U.S. (discussed above) had several important 

effects on soil survey. Through the use of quantitative class limits 

and diagnostic horizon definitions, all soil scientists, regardless of 

experience, were now able to classify soils correctly and consistently. 

Because of the need for data to properly classify the soil, the quality of 

field morphological descriptions was enhanced and efforts to obtain data 

measured in the laboratory increased. The use of Soil Taxonomy also 

improved the process of correlating soils from one soil survey project to 

another.

From the 1970s onward, much emphasis was devoted to the 

development of automated systems to store observations and manage 

data and interpretations, culminating in the National Soil Information 

System (NASIS). In addition, many soil surveys were digitized and made 

available electronically for use in geographic information systems. The 

development of digital soil information is discussed in greater detail in 

chapter 7.

In the mid-1970s, a new and important interest in soil survey 

emerged. The U.S Fish and Wildlife Service was charged with developing 

a wetland inventory of the United States. It partnered with the Soil Survey 

Division of the Soil Conservation Service to develop the concept and 

definition of “hydric soils” in support of the broader definition used to 

identify wetland areas for the inventory. Many established soil series were 

identified as likely to meet the definition of a hydric soil. The areas shown 

on soil survey maps that are composed of these soils were considered 

likely wetland areas for inclusion in the National Wetland Inventory. 

The soil survey became an important tool, along with other sources of 

hydrologic and vegetative information, for identifying wetlands for the 

inventory. A decade later, as a result of the Farm Bill passed by Congress 

in 1985, the demand for soil survey information increased further with 

the need to support the environmentally important “Swamp Buster” and 

“Sod Buster” provisions of the legislation. The soil survey maps and 
Soil Survey Manual 

information were crucial for identifying hydric soil areas as well as areas 

considered to be “highly erodible.” As a result, soil survey has been a 

major supporter of national efforts to protect and enhance the Nation’s 

resources. 

2000 and Onward

More recent efforts (since about 2000) to digitize all soil surveys 

and make them widely available through Internet access via the Web 

Soil Survey (Soil Survey Staff, 2016) have led to yet greater use of and 

demand for soil survey information for an ever wider group of users 

(see appendices). Now that users have electronic access to soil survey 

maps and information, the demand for hard-copy soil survey reports has 

decreased (see chapter 7 for a fuller discussion).

In addition to aerial photography, a wealth of multi-spectral data 

sources from airborne platforms and satellites have provided a wide range 

of remotely sensed information that can be used to infer the kinds and 

influence of soil-forming factors in digital soil mapping efforts (discussed 

in chapter 5). Noninvasive field tools, such as ground-penetrating radar, 

electromagnetic induction, portable X-ray fluorescence, and other 

proximal sensing technologies, also are being used to rapidly assess soil 

properties. These tools are discussed in greater detail in chapter 6.

A series of specialized interpretations have been developed for use 

by emergency response agencies. Soil information can be useful in 

providing rapid response to natural disasters and other civil emergencies. 

For example, it can be used to address oil spills or mass animal mortality 

in the agricultural sector (such as by avian flu) and the need to dispose of 

carcasses safely.

In the United States, after more than 100 years of soil survey work, 

nearly all of the Nation’s lands have been surveyed. The emphasis is no 

longer on making soil surveys where none existed but on maintaining 

and modernizing existing soil surveys. Technology and standards have 

evolved, and the kinds of information needed have changed. In addition, 

there remains an ongoing effort to better coordinate and join the 

individual soil surveys over large areas. The NCSS program is focused 

upon completing soil surveys for the few remaining unmapped areas 

and coordinating and updating existing soil surveys through correlation 

activities and data collection. It provides a cadre of trained soil scientists 

to assist soil survey users with the application of soil survey information 

for land resource management. The four fundamental goals guiding the 

NCSS program are: (1) completing the inventory of soils in the United 

States, (2) keeping the inventory current, (3) providing interpretive 
18 Chapter 

information about the soils, and (4) providing access to and promoting 

use of soil information. The NCSS motto is “Helping people understand 

soils.”

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