Soil

Related Topics:
Soils :: Soil_and_Additives :: Soil_Ecology :: Soil_Mineralogy :: Soil :: Soil_Fertility_and_Fertilizers :: Soil_and_Water :: Soil_Erosion :: Soils_and_Nutrition :: Soil_Morphology,_Classification_and_Survey

Soil is the complex body on the surface of a lithosphere subject to soil formation processes, comprised by mineral and organic matter, as well as living organisms.

Overview

Soil, comprising the pedosphere, is earthy material that has been affected by pedogenesis. The pedosphere is positioned at the interface of the lithosphere with the biosphere, atmosphere, and hydrosphere.

Soil forms through a variety of soil formation processes, and includes weathered rock "parent material" combined with dead and living organic matter and air. Soils are vital to all life on Earth because they support the growth of plants, which supply food and oxygen and absorb carbon dioxide and nitrogen.

Introduction

Soil is among our most important natural resources because of its position in the landscape and its dynamic physical, chemical, and biologic functions. Indeed, engineers, agronomists, chemists, geologists, geographers, biologists, microbiologists, sylviculturists, sanitarians, archaeologists, and specialists in regional planning, all depend on, and contribute to, knowledge of soils. While the general concept of soil is well established, the definition of soil varies, according to the perspective of the discipline or occupation using soil as a resource.

Soil occupies the pedosphere, one of Earth's spheres that the geosciences use to conceptually organise the Earth. This is the conceptual perspective of pedology and edaphology, the two main branches of soil science. 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.

The understanding of soil is incomplete. Despite the duration of mankind's dependence on and curiosity about soil, exploring the diversity and dynamic of this opaque resource continues to reward. New and refreshing avenues of soil research are compelled by our need to understand soil in the context of climate change Pielke, Roger (December 12, 2005) Is Soil an Important Component of the Climate System? The Climate Science Weblog. Url last accessed 2006-04-19, greenhouse gases Glomalin -- Summary Last updated 25 January 2006. CO₂ Science. Url last accessed 2006-04-19 Soil (stability) -- Summary. CO₂ Science. Url last accessed 2006-04-19, and carbon sequestration. Soil Carbon Sequestration. CO₂ Science. Url last accessed 2006-04-19

Vasily V. Dokuchaev, a Russian geographer, is credited with identifying soil as a resource whose distinctness and complexity deserved to be separated conceptually from geology and crop production and treated as a whole.

Previously, soil had been considered a product of physicochemical transformations of rocks, a dead substrate from which plants derive nutritious mineral 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. Krasilnikov, N.A. (1958) Soil Microorganisms and Higher Plants

Soil classification

Soil classification is a contentious subject, from the structure of the classification system itself, to the definitions of classes and types, and finally in the application in the field. Every classification system starts with its own individual definition of soil. The essential problem is that soils do not reproduce or have DNA like living organisms, so no "objective" criteria can be used to choose among classifications. The most qualified specialists in the world can and do spend hours during a field trip at each soil profile, arguing about the classification. Yet, in a well-constructed system, the different names refer to similar concepts, so that interpretations do not vary widely.

The FAO developed a supra-national classification, the FAO soil classification, also called World Soil Classification, which offers useful generalizations about soils pedogenesis in relation to the interactions with the main soil-forming factors. It was first published in form of the UNESCO Soil Map of the World (1974) (scale 1 : 5 M.). Many of the names offered in that classification are known in many countries and do have similar meanings. Originally developed as a legend to the Soil Map of the World, the classification has been applied by United Nations sponsored projects. Many countries have modified this system to fit their particular needs.

Vernacular classification systems

Vernacular soil classification systems are developed by the land users. Their structure 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.Vernacular Systems Url last accessed on 2006-04-18 A vernacular distinction familiar to many:

Heavy soils and light soils. Light soils have lower clay content than heavy soils. They often drain better and dry out sooner, giving them a lighter color. Lighter soils, with their lower moisture 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.

Soil characteristics

Soils vary widely in composition and structure from place to place. Soils are formed through weathering of minerals and organic matter. Weathering is the action of wind, rain, ice, sunlight and biological processes, which breaks parent material down into smaller particles and alters their chemistry. Soils form from weathering in place although many soils are comprised entirely of transported weathered material which arrives as flood sediments, eolian deposits, or dust fall. The proportions and types of minerals and organic matter help determine the characteristics of a particular soil.

Soils are also affected by human habitation. People can alter soils to make them more suitable for plant growth through the addition of organic materials and natural or synthetic fertilizer, and by improving their drainage or water-retaining capacity. Human actions also can degrade soils through the depletion of nutrients, pollution, soil contamination, and soil compaction, and by increasing the rate of erosion, which is the relocation of soil through the movement of water or wind.

Composition — Soil composed from solid, liquid and gas phases. Water and soil atmosphere are thus integral components of soils. Water occupies the void space between soil particles. Air occupies the remaining void space, if any. Both water and air components of soils are important to plant growth and other life in the soil profile of a particular ecosystem.
Soil texture — refers to soil grain size. According to U.S. system grades defined as follows: sand — 2 to 0.02 or 0.05 mm; silt — 0.02 or 0.05 to 0.002 mm; clay <0.002 mm. Soil texture influences available water capacity and movement, fertility, and workability or "tilth". "Loam" is a name for one of various mixtures of these three particle sizes. The ratio of these particles determines soil texture classification.
Soil structure – the arrangement of soil particles into aggregates, which may have various shapes, sizes and degrees of development or expression. Soil structure influences aeration, water movement, erosion resistance, and root penetration.

Soil color — Soil color often indicates soil moisture status and is used for determining hydric soils. Often described by using general terms, such as dark brown, yellowish brown, etc., soil colors are also described more technically by using Munsell soil color charts, which separate color into components of hue (relation to red, yellow and blue), value (lightness or darkness) and chroma (paleness or strength).
Soil chemistry — A complex subject within soil science; some characteristics are:
- Soil pH — The acidity or alkalinity of soils, which affects plant growth and soil fertility.
- Cation exchange capacity — The soil's ability to retain and exchange positively charged ions, which include major plant nutrients.
- Reduction and oxidation (Redox) reactions are also important.
The soil profile — A vertical cut that exposes soil layering or soil horizons. Horizons are formed by combined biological, chemical and physical alterations.
Permeability — The ability of a soil to transmit water or air. Faster or greater permeability often occurs in sandy or gravelly soils due to large pore spaces. Slower permeability typically occurs in finer textured clay soils, or compacted soils with little structure.
Drainage — The rate in which water is removed from a soil. Drainage influences most uses of soils, whether for agriculture, silviculture or urban. Classes of soil drainage are those found in soil survey reports, such as well drained, moderately well drained, somewhat poorly drained, poorly drained, and very poorly drained. Soil color patterns (such as mottle patterns or redoximorphic features) often indicate soil drainage class. The most productive agricultural soils are typically well drained or moderately well drained, as are the soils easiest to develop for urban use. By contrast, hydric soils are poorly or very poorly drained. A soil's natural drainage rate can be significantly increased by subsurface "tile" drainage.
Soil biology — Soils serve as habitats for soil organisms varying in size from microorganisms to small animals. The character of soils is intricately tied to bioturbation and the biochemical functions performed by soil organisms. The soil is home to a large proportion of the world's genetic diversity, which changes by soil type: desert soils (like aridisols) generally have more complex soil biotic communities and genetic diversity than tropical soils (like oxisols).
Soil smell — earthy odors are normally the product of microbial activity. Actinomycetes is responsible for the familiar smell associated with fresh turned garden soil and finished compost. At the other end of the pleasant/not-so-much memories scale is the rotton egg smell that deeply anaerobic microbial processes produce in wetland soils.
Soil tilth — Where soil mineral particles are both separated and bridged by organic matter breakdown products, and soil biota exudates, it makes the soil easy to work. Cultivation, earthworms, frost action and rodents mix the soil and decreases the size of the peds. This structure allows for good porosity and easy movement of air and water. This combination of ease in tillage, good moisture and air handling capabilities, and good structure for planting and germination, are definitive of the phrase good tilth

Soil and its environment

Soil in nature

An example of soil development from bare rock occurs on recent lava flows in warm regions under heavy and very frequent rainfall. In such climates plants become established very quickly on basaltic lava, even though there is very little organic material. The plants are supported by the porous rock becoming filled with nutrient bearing water, for example carrying dissolved bird droppings or guano. The developing plant roots themselves gradually breaks up the porous lava and organic matter soon accumulates but, even before it does, the predominantly porous broken lava in which the plant roots grow can be considered a soil.

Soil in everyday life

Gardening and landscaping provide common and popular experience with soils. Using compost and vermicompost are popular methods for diverting household waste for use to build soil fertility and tilth. The technique for creating Terra prêta do índio in the Amazon basin increasingly appears to have started from knowledge of soil first gained at a household-compost level.

Soil in agriculture

Agronomists study ways to make soils more productive. They test soils to determine whether they contain substances vital to plant growth. Such nutritional substances include compounds of organic matter, nitrogen, phosphorus, potassium, etc. If specific soil is deficient in these substances, fertilizers may provide them. Transport of nutrients through the soil, and the amount of nutrients absorbed by a plant's roots are investigated among other parameters.

Soil degradation

Soils are the critical component in land degradation. Types of land degradation are:

Desertification

Desertification is an environmental process of ecosystem degradation in arid and semi-arid regions, or as a result of human activity. It is a common misconception that droughts cause desertification. Droughts are common in arid and semiarid lands. Well-managed lands can recover from drought when the rains return. Continued land abuse during droughts, however, increases land degradation. Increased population and livestock pressure on marginal lands accelerates desertification.

Erosion

Soil erosional loss is caused by wind, water, ice, movement in response to gravity. Although the processes may be simultaneous, erosion is distinguished from weathering. Erosion is an intrinsic natural process, but in many places it is increased by human land use. Poor land use practices include deforestation, overgrazing, and improper construction activity. Improved management can limit erosion using techniques like limiting disturbance during construction, avoiding construction during erosion prone periods, intercepting runoff, terrace-building, use of erosion suppressing cover materials, and planting tress or other soil binding plants.

One of the main causes of soil erosion is slash and burn treatment of tropical forests. When the total ground surface is stripped of vegetation and then seared of all living organisms, the upper soils are vulnerable to both wind and water erosion. In a number of regions of the earth, entire sectors of a country have been rendered erosive; for example, on the Madagascar high central plateau, comprising approximately ten percent of that country's land area, virtually the entire landscape is sterile of vegetation, with gully erosive furrows typically in excess of 50 meters deep and one kilometer wide. Shifting cultivation is a farming system which sometimes incorporates the slash and burn method in some regions of the world. The resulting sediment load in rivers flowing to the west is ongoing, with most rivers a dark red brown colour.

Soil piping is a particular form of soil erosion that occurs below the soil surface. It is associated with levee and dam failure as well as sink hole formation. Turbulent flow removes soil starting from the mouth of the seep flow and subsoil erosion advances upgradient. The term sand boil is used to describe the appearance of the discharging end of an active soil pipe.

Soil acidification

Soil contamination

Derelict soils occur where industrial or other development activity damages the land to such a degree that it cannot be used safely or productively. Remediation of derelict soil uses pinciples of geology, physics, chemistry, and biology to degrade, attenuate, isolate, or remove soil contaminants and to restore soil functions and values. Techniques include leaching, air sparging, chemical amendments, phytoremediation, bioremediation, and natural attenuation.

Soil salination

Soil salination is the accumulation of free salts to such an extent that it leads to degradation of soils and vegetation.

Salination might be a natural process that results from:

high levels of salt in the soils
landscape features that allow salts to become mobile (movement of water table)
climatic trends that favor accumulation

Salt is a natural element of soils and water. The ions responsible for salination are: Na⁺, K⁺, Ca²⁺, Mg²⁺ and Cl^-

In some areas (for example in Australia), salinity is an inherent situation (enormous amounts of salts are stored in the soils). However, human practices have increased soil salinity by changing the natural balance of the water cycle, by allowing excess recharging of groundwater and accumulation through concentration.

One of the best examples of excess salination was observed in Egypt in 1970 when the Aswan High Dam was built. The change in the level of ground water before the construction had enabled soil erosion, which led to high concentration of salts in the water table. After the construction, the continuous high level of the water table led to the salination of the arable land.

Soil in archaeology

Soil examined in shovel test pits is used for relative dating based on stratigraphy (as opposed to absolute dating). Most typical is to use soil profile features to determine the maximum reasonable pit depth than needs to be examined for archaeological evidence in the interest of cultural resources management.

Soils altered or formed by man (anthropic and anthropogenic soils) are of interest to archaeologists. An example is Terra preta.

Soil in geology

Soil texture, color and chemistry often reflect the underlying geologic parent material and soil types often change at geologic unit boundaries.

Buried paleosols mark previous land surfaces and record climatic conditions from previous eras. Geologists use this paleopedological record to understand the ecological relationships in past ecosystems. For instance, geologic eras when conditions were conducive to forming deep, weathered soils were also associated with increasing ocean salinity and the formation of limestone. See biorhexistasy

Soil profile features are used to establish the duration of surface stability in the context of geologic faults or slope stability. An offset subsoil horizon indicates rupture during soil formation and the degree of subsequent subsoil formation is relied upon to establish time since rupture.

Pedology is the study of soils from the perspective of a geological timescale and many early soil scientists were trained as geologists. Today, geologists study soil for a better understanding of geology. As of 2002, geologists classify surface soils using the 1938 USDA soil taxonomy but use the current version of USDA soil taxonomy to classify buried paleosols.source: Paleopedological record

Soil in industry

Earthworks

Earth sheltering is the architectural practice of using soil for external thermal mass against building walls. The principle is that earthen material undergoes slow temperature changes and thus presents a fairly constant surface temperature at the wall. In higher latitudes with low average annual air temperature, the potential for heat leaching requires floor and base wall insulation. Earth based wall construction materials includes adobe, chirpici, cob, mudbrick, rammed earth, and sod. An earthen wall facing the mid-day sun can be designed as a trombe wall. A trombe wall is glazed on the exterior to enhance heat gain. Heat is vented to the interior at night.

Fuel

Peat deposits are found in many places around the world. The majority of peatlands are found in high latitudes; approximately 60% of the world's wetlands are peat. Peatlands cover around 3% of the global land mass or 3,850,000 to 4,100,000 km². Peat is available in considerable quantities in Scandinavia: some estimates put the amount of peat in Finland alone to be twice the size of North Sea oil reserves. Peat is used to produce both heat and electricity, often mixed with wood. Peat accounts for 6.2% of Finland's yearly energy production, second only to Ireland. Peat is arguably a slowly renewable biofuel but is more commonly classified as a fossil fuel. VAPO, a state-owned Finnish company, is among world leaders in peat production with approx. 9 million m^3/year as of 2004.

Overview

Introduction

Soil classification

Vernacular classification systems

Soil characteristics

Soil and its environment

Soil in nature

Soil in everyday life

Soil in agriculture

Soil degradation

Desertification

Erosion

Soil acidification

Soil contamination

Soil salination

Soil in archaeology

Soil in geology

Soil in industry

Earthworks

Fuel

Waste treatment

See also

References

Further reading and external links

Wikis

Gourt Home::Gourt :: Soil

Overview

Introduction

Soil classification

Vernacular classification systems

Soil characteristics

Soil and its environment

Soil in nature

Soil in everyday life

Soil in agriculture

Soil degradation

Desertification

Erosion

Soil acidification

Soil contamination

Soil salination

Soil in archaeology

Soil in geology

Soil in industry

Earthworks

Fuel

Waste treatment

See also

References

Further reading and external links

Wikis