Soil science

A soil scientist examines horizons within the soil profile

Soil Science is the overarching study of soil as a natural resource, including its functions, formation, classifications and the physical, chemical, biological, and fertility properties of soils. Ultimately, it is the study of soil for the use and management of soils.

There are many different disciplines in soil science, which is why often terms 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. But each of these only encompasses a very small part of what soil science covers. The diversity of displines that are either associated with or are reliant on this seemingly unimportant resource is varied. 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.

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.

Fields of study

Soil is characterised by geoscience as the pedosphere; the outer layer of Earth's subsystems. Beneath the pedosphere there are four more layers including the lithosphere, atmosphere, hydrosphere and biosphere. These layers make up the natural environment, and are just one of the many ways soil scientists try to categorise and understand soil.

There are two areas of study that are considered the main branches of soil science; pedology and edaphology. Pedology is the study of the way soil bodies form, evolve and the frameworks we use to understand and categorize them. Compared to edaphology this is a much more broad and longterm study of the way in which soil influences things. Edaphology is the study of soil and its influence on other living things, particularly plants.

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 occur within the pedosphere; more integrated, less soil-centric studies are also central. Many concepts essential to understanding soil come from individuals not identifiable strictly as soil scientists. This highlights the interdisciplinary nature of soil science.

Research

Dependence on and curiosity about soil, means scientists and organisations continue to explore the diversity and dynamics of this resource and continue to yield fresh new discoveries and insights. New avenues of soil research are compelled by a need to understand soil in the context of climate change, greenhouse gases, and carbon sequestration. 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. This includes subjects or research that may be very distantly related to soil, but it still pushes the field further.

Mapping

Main article: Soil survey

Most empirical knowledge of soil in nature comes from soil survey efforts. Soil survey, or soil mapping, is the process of determining the soil types or other properties of the soil cover over a landscape, and mapping them for others to understand and use. It relies heavily on distinguishing the individual influences of the five classic soil forming factors. This effort draws upon geomorphology, physical geography, and analysis of vegetation and land-use patterns. Primary data for the soil survey is acquired by field sampling and supported by remote sensing.

Classification

Main article: soil classification

Map of global soil regions from the USDA

As of 2006, the World Reference Base for Soil Resources, (WRB), developed by the International Union of Soil Science, is the pre-eminent soil classification system. It replaces the previous FAO soil classification that was developed by the Food and Agriculture Organization of the United Nations.

The WRB borrows from modern soil classification concepts, including USDA soil taxonomy. The classification is based mainly on soil morphology as an expression 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. 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.

History

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.

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 complexity and capabilities deserved to be separated conceptually from geology and crop production and treated as a whole seperate other thing. Fallou is considered one of the founding fathers of soil science, and was working on the very beginings of soil science 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 element; soil and bedrock were equated. But Dokuchaev considered 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 body actually known as soil by scientists is considered a very different material than bedrock. The latter becomes soil under the influence of a series of soil-formation factors (climate, topography, organisms, relief and time). According to Dokuchaev, 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, minerals and various kinds of living and dead organisms.

A 1914 encyclopedic definition: "the different forms of earth on the surface of the rocks, formed by the breaking down or weathering of rocks". 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. 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".

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, and the resultant desire to exploit or sustain the land that supports us. Often the distinctions between the sub-disciplines of soil science blur in the process of research, which is why they all fit under the umbrella of soil science. Scientists and associated 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 micro-biotic crusts and exploring the potential to sequester atmospheric carbon in soil organic matter. This is directly applicable too many areas of industry and production, the main being agriculture. A huge majority of research projects are specifically to make agriculture more sustainable, efficient and effective.

Soil science in this context, 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 often been to map soils. Only a very limited number of areas in the United States don't have a highly detailed soil survey, but the WRB as a worldwide index means the entire world has at least some level of classification, even if it is only the most broad and basic level. The soil survey 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:

• Land-based treatment of wastes
  • Septic system
  • Manure
  • Municipal biosolids
  • Food and fiber processing waste
• Identification and protection of environmentally critical areas
  • Sensitive and unstable soils
  • Wetlands
  • Unique soil situations that support valuable habitat, and ecosystem diversity
• Management for optimum land productivity
  • Silviculture
  • Agronomy
    • Nutrient management
    • Water management
  • Native vegetation
  • Grazing
• Management for optimum water quality
  • Stormwater management
  • Sediment and erosion control
• Remediation and restoration of damaged lands
  • Mine reclamation
  • Flood and storm damage
  • Contamination
• Sustainability of desired uses
  • Soil conservation

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

• Radiometric dating: specifically a knowledge of local pedology is used to date prior activity at the site
  • Stratification (archeology) where soil formation processes and preservative qualities can inform the study of archaeological sites
  • Geological phenomena
    • Landslides
    • Active faults
• Altering soils to achieve new uses
  • Vitrification to contain radioactive wastes
  • Enhancing soil microbial capabilities in degrading contaminants (bioremediation).
  • Carbon sequestration
  • Environmental soil science
• Pedology
  • Soil genesis
  • Pedometrics
  • Soil morphology
    • Soil micromorphology
  • Soil classification
    • USDA soil taxonomy
    • World Reference Base
• Soil biology
  • Soil microbiology
• Soil chemistry
  • Soil biochemistry
  • Soil mineralogy
• Soil physics
  • Pedotransfer function
  • Soil mechanics and engineering
• Soil hydrology, hydropedology

Fields of application in soil science

• Climate change
• Ecosystem studies
• Pedotransfer function
• Soil fertility / Nutrient management
• Soil management
• Soil survey
• Standard methods of analysis
• Watershed and wetland studies

Related disciplines

• Agricultural sciences
  • Agricultural soil science
  • Agrophysics science
  • Irrigation management
• Anthropology
  • archaeological stratigraphy
• Environmental science
  • Landscape ecology
• Physical geography
  • Geomorphology
• Geology
  • Biogeochemistry
  • Geomicrobiology
• Hydrology
  • Hydrogeology
• Waste management
• Wetland 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 overflowing. 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

• Agricultural soil science
• Agroecology
• Agrology
• Agrophysics
• Australian Society of Soil Science Incorporated (ASSSI)
• Compost
• History of soil science
• International Soil Reference and Information Centre (ISRIC)
• International Union of Soil Sciences (IUSS)
• Liming (soil)
• List of Russian Earth scientists
• List of State Soil Science Associations
• List of State Soil Science Licensing Boards
• National Society of Consulting Soil Scientists (NSCSS)
• Resonant column test
• Soil biology
• Soil Science Society of America (SSSA)
• Soil value
• World Congress of Soil Science (WCSS)

References

• 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.
• Marion LeRoy Jackson (2005). Soil Chemical Analysis: Advanced Course. UW-Madison Libraries Parallel Press. pp. 5–. ISBN 978-1-893311-47-3.