Soil science

Last updated

Soil scientist examining horizons within a soil profile Soil sci.jpg
Soil scientist examining horizons within a soil profile

Soil science is the study of soil as a natural resource on the surface of the Earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to the use and management of soils. [1]


Sometimes terms which refer to branches of soil science, such as pedology (formation, chemistry, morphology, and classification of soil) and edaphology (how soils interact with living things, especially plants), are used as if synonymous with soil science. The diversity of names associated with this discipline is related to the various associations concerned. Indeed, engineers, agronomists, chemists, geologists, physical geographers, ecologists, biologists, microbiologists, silviculturists, sanitarians, archaeologists, and specialists in regional planning, all contribute to further knowledge of soils and the advancement of the soil sciences. [1]

Soil scientists have raised concerns about how to preserve soil and arable land in a world with a growing population, possible future water crisis, increasing per capita food consumption, and land degradation. [2]

Fields of study

Soil occupies the pedosphere, one of Earth's spheres that the geosciences use to organize the Earth conceptually. This is the conceptual perspective of pedology and edaphology, the two main branches of soil science. Pedology is the study of soil in its natural setting. Edaphology is the study of soil in relation to soil-dependent uses. Both branches apply a combination of soil physics, soil chemistry, and soil biology. Due to the numerous interactions between the biosphere, atmosphere and hydrosphere that are hosted within the pedosphere, more integrated, less soil-centric concepts are also valuable. Many concepts essential to understanding soil come from individuals not identifiable strictly as soil scientists. This highlights the interdisciplinary nature of soil concepts.


Dependence on and curiosity about soil, exploring the diversity and dynamics of this resource continues to yield fresh discoveries and insights. New avenues of soil research are compelled by a need to understand soil in the context of climate change, [3] [4] greenhouse gases, and carbon sequestration. [3] Interest in maintaining the planet's biodiversity and in exploring past cultures has also stimulated renewed interest in achieving a more refined understanding of soil.


Soil survey, soil mapping, is the process of classifying soil types and other soil properties in a given area and geo-encoding such information. It applies the principles of soil science, and draws heavily from geomorphology, theories of soil formation, physical geography, and analysis of vegetation and land use patterns. Primary data for the soil survey are acquired by field sampling and by remote sensing. Remote sensing principally uses aerial photography, but LiDAR and other digital techniques are steadily gaining in popularity. In the past, a soil scientist would take hard-copies of aerial photography, topo-sheets, and mapping keys into the field with them. Today, a growing number of soil scientists bring a ruggedized tablet computer and GPS into the field with them. The tablet may be loaded with digital aerial photos, LiDAR, topography, soil geodatabases, mapping keys, and more.

The term soil survey may also be used as a noun to describe the published results. In the United States, these surveys were once published in book form for individual counties by the National Cooperative Soil Survey. Today, soil surveys are no longer published in book form; they are published to the web and accessed on NRCS Web Soil Survey where a person can create a custom soil survey. This allows for rapid flow of the latest soil information to the user. In the past it could take years to publish a paper soil survey. Today it takes only moments for changes to go live to the public. Also, the most current soil survey data is made available on the Download Soils Data tab at NRCS Web Soil Survey for high end GIS users such as professional consulting companies and universities.

The information in a soil survey can be used by farmers and ranchers to help determine whether a particular soil type is suited for crops or livestock and what type of soil management might be required. An architect or engineer might use the engineering properties of a soil to determine whether it is suitable for a certain type of construction. A homeowner may even use the information for maintaining or constructing their garden, yard, or home.

Soil survey information can be used to predict or estimate the potentials and limitations of soils for many specific uses. A soil survey includes an important part of the information that is used to make workable plans for land management. The information must be interpreted to be usable by professional planners and others. Predictions based on soil surveys serve as a basis for judgment about land use and management for areas ranging from small tracts to regions of several million acres. These predictions, however, must be evaluated along with economic, social, and environmental considerations before they can be used to make valid recommendations for land use and management. [5]


Map of global soil regions from the USDA Global soils map USDA.jpg
Map of global soil regions from the USDA

In 1998, the World Reference Base for Soil Resources (WRB) replaced the FAO soil classification as the international soil classification system. The currently valid version of WRB is the 4th edition, 2022. [6] The FAO soil classification, in turn, borrowed from modern soil classification concepts, including USDA soil taxonomy.

WRB is based mainly on soil morphology as an expression of pedogenesis. A major difference with USDA soil taxonomy is that soil climate is not part of the system, except insofar as climate influences soil profile characteristics.

Many other classification schemes exist, including vernacular systems. The structure in vernacular systems are either nominal, giving unique names to soils or landscapes, or descriptive, naming soils by their characteristics such as red, hot, fat, or sandy. Soils are distinguished by obvious characteristics, such as physical appearance (e.g., color, texture, landscape position), performance (e.g., production capability, flooding), and accompanying vegetation. [7] A vernacular distinction familiar to many is classifying texture as heavy or light. Light soil content and better structure, take less effort to turn and cultivate. Contrary to popular belief, light soils do not weigh less than heavy soils on an air dry basis nor do they have more porosity.


The earliest known soil classification system comes from China, appearing in the book Yu Gong (5th century BCE), where the soil was divided into three categories and nine classes, depending on its color, texture and hydrology. [8]

Contemporaries Friedrich Albert Fallou, the German founder of modern soil science, and Vasily Dokuchaev, the Russian founder of modern soil science, are both credited with being among the first to identify soil as a resource whose distinctness and complexity deserved to be separated conceptually from geology and crop production and treated as a whole. As a founding father of soil science Fallou has primacy in time. Fallou was working on the origins of soil before Dokuchaev was born, however Dokuchaev's work was more extensive and is considered to be the more significant to modern soil theory than Fallou's.

Previously, soil had been considered a product of chemical transformations of rocks, a dead substrate from which plants derive nutritious elements. Soil and bedrock were in fact equated. Dokuchaev considers the soil as a natural body having its own genesis and its own history of development, a body with complex and multiform processes taking place within it. The soil is considered as different from bedrock. The latter becomes soil under the influence of a series of soil-formation factors (climate, vegetation, country, relief and age). According to him, soil should be called the "daily" or outward horizons of rocks regardless of the type; they are changed naturally by the common effect of water, air and various kinds of living and dead organisms. [9]

A 1914 encyclopedic definition: "the different forms of earth on the surface of the rocks, formed by the breaking down or weathering of rocks". [10] serves to illustrate the historic view of soil which persisted from the 19th century. Dokuchaev's late 19th century soil concept developed in the 20th century to one of soil as earthy material that has been altered by living processes. [11] A corollary concept is that soil without a living component is simply a part of earth's outer layer.

Further refinement of the soil concept is occurring in view of an appreciation of energy transport and transformation within soil. The term is popularly applied to the material on the surface of the Earth's moon and Mars, a usage acceptable within a portion of the scientific community. Accurate to this modern understanding of soil is Nikiforoff's 1959 definition of soil as the "excited skin of the sub aerial part of the earth's crust". [12]

Areas of practice

Academically, soil scientists tend to be drawn to one of five areas of specialization: microbiology, pedology, edaphology, physics, or chemistry. Yet the work specifics are very much dictated by the challenges facing our civilization's desire to sustain the land that supports it, and the distinctions between the sub-disciplines of soil science often blur in the process. Soil science professionals commonly stay current in soil chemistry, soil physics, soil microbiology, pedology, and applied soil science in related disciplines

One interesting effort drawing in soil scientists in the USA as of 2004 is the Soil Quality Initiative. Central to the Soil Quality Initiative is developing indices of soil health and then monitoring them in a way that gives us long term (decade-to-decade) feedback on our performance as stewards of the planet. The effort includes understanding the functions of soil microbiotic crusts and exploring the potential to sequester atmospheric carbon in soil organic matter. The concept of agriculture in relation to soil quality, however, has not been without its share of controversy and criticism, including critiques by Nobel Laureate Norman Borlaug and World Food Prize Winner Pedro Sanchez.

A more traditional role for soil scientists has been to map soils. Most every area in the United States now has a published soil survey, which includes interpretive tables as to how soil properties support or limit activities and uses. An internationally accepted soil taxonomy allows uniform communication of soil characteristics and soil functions. National and international soil survey efforts have given the profession unique insights into landscape scale functions. The landscape functions that soil scientists are called upon to address in the field seem to fall roughly into six areas:

There are also practical applications of soil science that might not be apparent from looking at a published soil survey.

Fields of application in soil science

Depression storage capacity

Depression storage capacity, in soil science, is the ability of a particular area of land to retain water in its pits and depressions, thus preventing it from flowing. [13] Depression storage capacity, along with infiltration capacity, is one of the main factors involved in Horton overland flow, whereby water volume surpasses both infiltration and depression storage capacity and begins to flow horizontally across land, possibly leading to flooding and soil erosion. The study of land's depression storage capacity is important in the fields of geology, ecology, and especially hydrology.

See also

Related Research Articles

<span class="mw-page-title-main">Pedology</span> Study of soils in their natural environment

Pedology is a discipline within soil science which focuses on understanding and characterizing soil formation, evolution, and the theoretical frameworks for modeling soil bodies, often in the context of the natural environment. Pedology is often seen as one of two main branches of soil inquiry, the other being edaphology which is traditionally more agronomically oriented and focuses on how soil properties influence plant communities. In studying the fundamental phenomenology of soils, e.g. soil formation, pedologists pay particular attention to observing soil morphology and the geographic distributions of soils, and the placement of soil bodies into larger temporal and spatial contexts. In so doing, pedologists develop systems of soil classification, soil maps, and theories for characterizing temporal and spatial interrelations among soils. There are a few noteworthy sub-disciplines of pedology; namely pedometrics and soil geomorphology. Pedometrics focuses on the development of techniques for quantitative characterization of soils, especially for the purposes of mapping soil properties whereas soil geomorphology studies the interrelationships between geomorphic processes and soil formation.

<span class="mw-page-title-main">Aridisol</span>

Arid soils are a soil order in USDA soil taxonomy. Aridisols form in an arid or semi-arid climate. Aridisols dominate the deserts and xeric shrublands, which occupy about one third of the Earth's land surface. Aridisols have a very low concentration of organic matter, reflecting the paucity of vegetative production on these dry soils. Water deficiency is the major defining characteristic of Aridisols. Also required is sufficient age to exhibit subsoil weathering and development. Limited leaching in aridisols often results in one or more subsurface soil horizons in which suspended or dissolved minerals have been deposited: silicate clays, sodium, calcium carbonate, gypsum or soluble salts. These subsoil horizons can also be cemented by carbonates, gypsum or silica. Accumulation of salts on the surface can result in salinization.

<span class="mw-page-title-main">Oxisol</span> Soil type known for occurring in tropical rain forests

Oxisols are a soil order in USDA soil taxonomy, best known for their occurrence in tropical rain forest within 25 degrees north and south of the Equator. In the World Reference Base for Soil Resources (WRB), they belong mainly to the ferralsols, but some are plinthosols or nitisols. Some oxisols have been previously classified as laterite soils.

<span class="mw-page-title-main">Chernozem</span> Soil type; very fertile, black-coloured soil containing a high percentage of humus

Chernozem, also called black soil, is a black-colored soil containing a high percentage of humus and high percentages of phosphorus and ammonia compounds. Chernozem is very fertile soil and can produce high agricultural yields with its high moisture storage capacity. Chernozems are a Reference Soil Group of the World Reference Base for Soil Resources (WRB).

<span class="mw-page-title-main">Soil classification</span> Systematic categorization of soils

Soil classification deals with the systematic categorization of soils based on distinguishing characteristics as well as criteria that dictate choices in use.

<span class="mw-page-title-main">Gelisol</span> Permafrost soils

Gelisols are an order in USDA soil taxonomy. They are soils of very cold climates which are defined as containing permafrost within two meters of the soil surface. The word "Gelisol" comes from the Latin gelare meaning "to freeze", a reference to the process of cryoturbation that occurs from the alternating thawing and freezing characteristic of Gelisols.

<span class="mw-page-title-main">Andisol</span> Soils formed in volcanic ash and containing glass and amorphous colloidal materials

In USDA soil taxonomy, Andisols are soils formed in volcanic ash and defined as soils containing high proportions of glass and amorphous colloidal materials, including allophane, imogolite and ferrihydrite. In the World Reference Base for Soil Resources (WRB), Andisols are known as Andosols.

In USDA soil taxonomy, a Psamment is defined as an Entisol which consists basically of unconsolidated sand deposits, often found in shifting sand dunes but also in areas of very coarse-textured parent material subject to millions of years of weathering. This latter case is characteristic of the Guiana Highlands of northern South America. A Psamment has no distinct soil horizons, and must consist entirely of material of loamy sand or coarser in texture. In the World Reference Base for Soil Resources (WRB), Psamments are known as Arenosols.

This is an index of articles relating to soil.

<span class="mw-page-title-main">Gypsisol</span>

Gypsisols in the World Reference Base for Soil Resources (WRB) are soils with substantial secondary accumulation of gypsum (CaSO4.2H2O). They are found in the driest parts of the arid climate zone. In the USDA soil taxonomy they are classified as Gypsids (USDA Soil Taxonomy), in the Russian soil classification they are called Desert soils (USSR).

<span class="mw-page-title-main">Acrisol</span>

An Acrisol is a Reference Soil Group of the World Reference Base for Soil Resources (WRB). It has a clay-rich subsoil and is associated with humid, tropical climates, such as those found in Brazil, and often supports forested areas. In the USDA soil taxonomy, Acrisols correspond to the Humult, Udult and Ustult suborders of the Ultisols and also to Oxisols with a kandic horizon and to some Alfisols. The Acrisols low fertility and toxic amounts of aluminium pose limitations to its agricultural use, favouring in many places its use for silviculture, low intensity pasture and protected areas. Crops that can be successfully cultivated, if climate allows, include tea, rubber tree, oil palm, coffee and sugar cane.

The early concepts of soil were based on ideas developed by a German chemist, Justus von Liebig (1803–1873), and modified and refined by agricultural scientists who worked on samples of soil in laboratories, greenhouses, and on small field plots. The soils were rarely examined below the depth of normal tillage. These chemists held the "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 in manure, lime, and fertilizer.

<span class="mw-page-title-main">Cambisol</span> Type of soil

A Cambisol in the World Reference Base for Soil Resources (WRB) is a soil in the beginning of soil formation. The horizon differentiation is weak. This is evident from weak, mostly brownish discolouration and/or structure formation in the soil profile.

<span class="mw-page-title-main">Regosol</span> Highly Weathered Soil

A Regosol in the World Reference Base for Soil Resources (WRB) is very weakly developed mineral soil in unconsolidated materials. Regosols are extensive in eroding lands, in particular in arid and semi-arid areas and in mountain regions. Internationally, Regosols correlate with soil taxa that are marked by incipient soil formation such as Entisols in the USDA soil taxonomy or Rudosols and possibly some Tenosols in the Australian Soil Classification.

<span class="mw-page-title-main">Planosol</span> Soil type

A Planosol in the World Reference Base for Soil Resources is a soil with a light-coloured, coarse-textured, surface horizon that shows signs of periodic water stagnation and abruptly overlies a dense, slowly permeable subsoil with significantly more clay than the surface horizon. In the US Soil Classification of 1938 used the name Planosols, whereas its successor, the USDA soil taxonomy, includes most Planosols in the Great Groups Albaqualfs, Albaquults and Argialbolls.

<span class="mw-page-title-main">Andosol</span> Soils formed in volcanic ash and containing glass and amorphous colloidal materials

Andosols are soils found in volcanic areas formed in volcanic tephra. In some cases Andosols can also be found outside active volcanic areas. Andosols cover an estimated 1–2% of earth's ice-free land surface. Andosols are a Reference Soil Group of the World Reference Base for Soil Resources (WRB). They are closely related to other types of soils such as Vitrosols, Vitrandosols, Vitrons and Pumice Soils that are used in different soil classification systems. Poorly developed Andosols are often rich in vitreous materials and are therefore also called Vitric Andosols. The name comes from Japanese an and do, synonymous with kuroboku. In the USDA soil taxonomy, Andosols are known as Andisols.

<span class="mw-page-title-main">Fluvisol</span>

A fluvisol in the World Reference Base for Soil Resources (WRB) is a genetically young soil in alluvial deposits. Apart from river sediments, they also occur in lacustrine and marine deposits. Fluvisols correlate with fluvents and fluvaquents of the USDA soil taxonomy. The good natural fertility of most fluvisols and their attractive dwelling sites on river levees and higher parts in marine landscapes were recognized in prehistoric times.

<span class="mw-page-title-main">Nitisol</span>

A nitisol in the World Reference Base for Soil Resources (WRB) is a deep, red, well-drained soil with a clay content of more than 30% and a blocky structure. Nitisols correlate with the kandic alfisols, ultisols and inceptisols of the USDA soil taxonomy.

<span class="mw-page-title-main">Phaeozem</span> Type of soil

A Phaeozem in the World Reference Base for Soil Resources (WRB) is a dark soil with a high base status, but without a secondary carbonates within one metre of the soil surface. Phaeozems correlate with the Udolls and Aquolls (Mollisols) of the USDA soil taxonomy.

<span class="mw-page-title-main">Friedrich Albert Fallou</span>

Friedrich Albert Fallou (1794–1877) was the German founder of modern soil science. While working as a lawyer and tax assessor, Fallou established himself as an independent scientist, a recognized authority in the natural history of farm and forest soil. In 1862 he advanced the idea that soil was separate in nature from geology. Intent on establishing the study of soils as an independent science, Fallou introduced the term pedology.


  1. 1 2 Jackson, J. A. (1997). Glossary of Geology (4. ed.). Alexandria, Virginia: American Geological Institute. p 604. ISBN   0-922152-34-9
  2. H. H. Janzen; et al. (2011). "Global Prospects Rooted in Soil Science". Soil Science Society of America Journal. 75 (1): 1. Bibcode:2011SSASJ..75....1J. doi:10.2136/sssaj2009.0216.
  3. 1 2 3 Ochoa-Hueso, R; Delgado-Baquerizo, M; King, PTA; Benham, M; Arca, V; Power, SA (February 2019). "Ecosystem type and resource quality are more important than global change drivers in regulating early stages of litter decomposition". Soil Biology and Biochemistry. 129: 144–152. doi:10.1016/j.soilbio.2018.11.009. S2CID   92606851.
  4. Pielke, Roger (12 December 2005). "Is Soil an Important Component of the Climate System?". The Climate Science Weblog. Archived from the original on 8 September 2006. Retrieved 19 April 2012.
  5. "Soil Survey". NRCS Nebraska. US Department of Agriculture. Retrieved 5 September 2019.PD-icon.svg This article incorporates text from this source, which is in the public domain .
  6. 1 2 IUSS Working Group WRB (2022). "World Reference Base for Soil Resources, 4th edition". IUSS, Vienna.
  7. "Vernacular Systems". Archived from the original on 6 March 2007. Retrieved 19 April 2012.
  8. Arnold, R. et al. (2009) A Handbook of Soil Terminology, Correlation and Classification Earthscan, London, England.
  9. Krasilnikov, N.A. (1958) Soil Microorganisms and Higher Plants Archived 12 November 2004 at the Wayback Machine
  10. Wikisource:The New Student's Reference Work/4-0310
  11. Buol, S. W.; Hole, F. D. & McCracken, R. J. (1973). Soil Genesis and Classification (First ed.). Ames, IA: Iowa State University Press. ISBN   978-0-8138-1460-5..
  12. C. C. Nikiforoff (1959). "Reappraisal of the soil: Pedogenesis consists of transactions in matter and energy between the soil and its surroundings". Science. 129 (3343): 186–196. Bibcode:1959Sci...129..186N. doi:10.1126/science.129.3343.186. PMID   17808687.
  13. Hansen, Bjarne, Per Schjønning, and Erik Sibbesen. "Roughness indices for estimation of depression storage capacity of tilled soil surfaces Archived 25 August 2017 at the Wayback Machine ." Soil and Tillage Research 52.1 (1999): 103-111.