The main branches of soil science arepedology ― the study of formation, chemistry, morphology, and classification of soil ― andedaphology ― the study of how soils interact with living things, especially plants. Sometimes terms which refer to those branches 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 inregional 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 futurewater crisis, increasing per capitafood consumption, andland degradation.[2]
Soil occupies thepedosphere, one ofEarth's spheres that thegeosciences use to organize the Earth conceptually. This is the conceptual perspective ofpedology andedaphology, 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 ofsoil physics,soil chemistry, andsoil biology. Due to the numerous interactions between thebiosphere,atmosphere andhydrosphere 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.
Exploring the diversity and dynamics of soil continues to yield fresh discoveries and insights. New avenues of soil research are compelled by a need to understand soil in the context ofclimate change,[3][4]greenhouse gases, andcarbon sequestration.[3] Interest in maintaining the planet's biodiversity and in exploringpast cultures has also stimulated renewed interest in achieving a more refined understanding of soil.
WRB is based mainly onsoil morphology as an expression ofpedogenesis. 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 is 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.[6] 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. Light soils do not necessarily weigh less than heavy soils on an air dry basis, nor do they have moreporosity.
The earliest knownsoil classification system comes from China, appearing in the bookYu Gong (5th century BCE), where the soil was divided into three categories and nine classes, depending on its color, texture and hydrology.[7]
ContemporariesFriedrich Albert Fallou (the German founder of modern soil science) andVasily 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 andbedrock 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.[8]
A 1914 encyclopedic definition: "the different forms of earth on the surface of the rocks, formed by the breaking down orweathering of rocks".[9] 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.[10] 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 thematerial 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 theEarth's crust".[11]
Academically, soil scientists tend to be drawn to one of five areas of specialization:microbiology,pedology,edaphology,physics, orchemistry. 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 exciting effort drawing in soil scientists in the U.S. as of 2004[update] 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 insoil organic matter. Relating the concept of agriculture tosoil quality, however, has not been without its share of controversy and criticism, including critiques by Nobel LaureateNorman Borlaug and World Food Prize WinnerPedro Sanchez.
A more traditional role for soil scientists has been to map soils. Almost every area in the United States now has a publishedsoil survey, including interpretive tables on how soil properties support or limit activities and uses. An internationally accepted soil taxonomy allows uniform communication of soil characteristics andsoil 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:
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.[12] Depression storage capacity, along withinfiltration capacity, is one of the main factors involved inHorton overland flow, whereby water volume surpasses both infiltration and depression storage capacity and begins to flow horizontally across land, possibly leading toflooding andsoil erosion. The study of land's depression storage capacity is important in the fields ofgeology,ecology, and especiallyhydrology.
^abcOchoa-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.Bibcode:2019SBiBi.129..144O.doi:10.1016/j.soilbio.2018.11.009.hdl:10261/336676.S2CID92606851.
^Buol, S. W.; Hole, F. D. & McCracken, R. J. (1973).Soil Genesis and Classification (First ed.). Ames, IA: Iowa State University Press.ISBN978-0-8138-1460-5..
Soil Survey Staff (1993).Soil Survey: Early Concepts of Soil. (html)Soil Survey Manual USDA Handbook 18, Soil Conservation Service. U.S. Department of Agriculture. URL accessed on 2004-11-30.
