Sandy soil. The first type of soil is the sand. It consists of small particles of weathered rock.
Silty Soil. Silt, which is known to have much smaller particles compared to...Clay Soil. Clay is the smallest particles amongst the other two types of soil.

Loamy Soil. Loam is the fourth types of soil.The ground on which we walk is never quite the same, it keeps on changing. Sometimes it is made up of millions of tiny granules and other times it is the hard surface of tar covered roads. There was the time long back when this ground was mostly covered with soil and grass. And then came the roads, rails and so on. This soil is a very broad term and refers to a loose layer of earth that covers the surface of the planet.

The soil is the part of the earth’s surface which includes disintegrated rock, humus, inorganic and other organic materials that provides the medium for plants growth. For the formation of soil, it takes around hundreds to thousands of years. The soil is usually generated when rocks break up into their constituent parts. When a range of different forces acts on the rocks, they break into smaller parts to form the soil. These forces also include the impact of wind, water and the reaction from saltsAbout land and soil information 

 Having accurate and accessible information about land and soil helps us to manage them in the most productive and sustainable way. 

Why is land and soil information important?

Soils are an important, non-renewable natural resource. Healthy soils support a healthy environment: they support plant and animal productivity and biodiversity, promote water and air quality and underpin our food and fibre supplies, so they are vital for our survival.

To productively and sustainably manage our land and soils, we need to know where our best and worst landscapes and soils are, and what we can do with them without causing degradation. For this, we need a comprehensive, high-quality, accessible resource of soil and land information.

What information do we hold?

OEH collects and manages two major types of soil and land information.

Soil profiles

A soil profile is a column of soil going vertically downwards from the surface to a certain depth at a particular location. This column of soil is described and tested, including (in some cases) collection of samples for testing at a laboratory.

The soil description and test results, along with features of the site and local area, are recorded in the NSW Soil and Land Information System (SALIS), a database of soil information from across NSW that is managed by Office of Environment and Heritage (OEH). Contextual information may include assessments of:

More than 73,000 profiles are stored in SALIS, of which about two-thirds are publicly available. The information is collected by OEH field staff and many other contributors, who add thousands of collection points each year.

Landscape and soil mapping

We map soils and landscapes to understand their distribution, the processes by which they develop, their capability and suitability for various uses, what risks may be involved and how they can be safely addressed.

This information is important for both the direct users of land and soils and for more strategic purposes, such as planning and policy-making, environmental protection, and improvement of or adaptation to large-scale environmental problems such as climate change, soil erosion, acidification and dryland salinity. Recently, OEH’s soil and landscape mapping has provided the foundation for the NSW Government’s identification of the State’s best land and soils through its mapping of Biophysical Strategic Agricultural Land.

Office of Environment and Heritage manages mapping from a number of programs, collected in various areas of NSW at different scales for various purposes. An increasing majority of these datasets are stored in SALIS and available on eSPADE. You can find more information about them on the soil maps of NSW page.

How do we manage land and soil information?

Office of Environment and Heritage has developed a suite of online systems for collecting, storing and accessing soil and land information.For other uses, see Soil (disambiguation).

mixture of organic matter, minerals, gases, liquids, and organisms that together support life

 | Look up  soil in Wiktionary, the free dictionary.

A, B, and C represent the soil profile, a notation firstly coined by Vasily Dokuchaev (1846–1903), the father of pedology; A is the topsoil; B is a regolith; C is a saprolite (a less-weathered regolith); the bottom-most layer represents the bedrock.

Surface-water-gley developed in glacial till, Northern Ireland.

Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Earth's body of soil, called the pedosphere, has four important functions: 

All of these functions, in their turn, modify the soil. 

The pedosphere interfaces with the lithosphere, the hydrosphere, the atmosphere, and the biosphere.^[1] The term pedolith, used commonly to refer to the soil, translates to ground stone in the sense "fundamental stone".^[2] Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution).^[3][4][5] Accordingly, soil scientists can envisage soils as a three-state system of solids, liquids, and gases.^[6]

Soil is a product of several factors: the influence of climate, relief (elevation, orientation, and slope of terrain), organisms, and the soil's parent materials (original minerals) interacting over time.^[7] It continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem.^[8]

Most soils have a dry bulk density (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm³, while the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm³.^[9] Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic,^[10] although fossilized soils are preserved from as far back as the Archean.^[11]

Soil science has two basic branches of study: edaphology and pedology. Edaphology studies the influence of soils on living things.^[12] Pedology focuses on the formation, description (morphology), and classification of soils in their natural environment.^[13] In engineering terms, soil is included in the broader concept of regolith, which also includes other loose material that lies above the bedrock, as can be found on the Moon and on other celestial objects as well.^[14] Soil is also commonly referred to as earth or dirt; some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil.^[15]

Contents

Overview[edit]

Soil Profile: Darkened topsoil and reddish subsoil layers are typical in some regions.

Functions[edit]

Soil is a major component of the Earth's ecosystem. The world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, from ozone depletion and global warming to rainforest destruction and water pollution. With respect to Earth's carbon cycle, soil is an important carbon reservoir, and it is potentially one of the most reactive to human disturbance^[16] and climate change.^[17] As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures, a positive feedback (amplification).^[18] This prediction has, however, been questioned on consideration of more recent knowledge on soil carbon turnover.^[19]

Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, and a medium for plant growth, making it a critically important provider of ecosystem services.^[20] Since soil has a tremendous range of available niches and habitats, it contains most of the Earth's genetic diversity. A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial and in the main still unexplored.^[21][22] Soil has a mean prokaryotic density of roughly 10⁸ organisms per gram,^[23] whereas the ocean has no more than 10⁷ procaryotic organisms per milliliter (gram) of seawater.^[24] Organic carbon held in soil is eventually returned to the atmosphere through the process of respiration carried out by heterotrophic organisms, but a substantial part is retained in the soil in the form of soil organic matter; tillage usually increases the rate of soil respiration, leading to the depletion of soil organic matter.^[25] Since plant roots need oxygen, ventilation is an important characteristic of soil. This ventilation can be accomplished via networks of interconnected soil pores, which also absorb and hold rainwater making it readily available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the water-holding capacity of soils is vital for plant survival.^[26]

Soils can effectively remove impurities,^[27] kill disease agents,^[28] and degrade contaminants, this latter property being called natural attenuation.^[29] Typically, soils maintain a net absorption of oxygen and methane and undergo a net release of carbon dioxide and nitrous oxide.^[30] Soils offer plants physical support, air, water, temperature moderation, nutrients, and protection from toxins.^[31] Soils provide readily available nutrients to plants and animals by converting dead organic matter into various nutrient forms.^[32]

Description[edit]

Components of a loam soil by percent volume 

  Water (25%)

  Gases (25%)

  Sand (18%)

  Silt (18%)

  Clay (9%)

  Organic matter (5%)

A typical soil is about 50% solids (45% mineral and 5% organic matter), and 50% voids (or pores) of which half is occupied by water and half by gas.^[33] The percent soil mineral and organic content can be treated as a constant (in the short term), while the percent soil water and gas content is considered highly variable whereby a rise in one is simultaneously balanced by a reduction in the other.^[34] The pore space allows for the infiltration and movement of air and water, both of which are critical for life existing in soil.^[35] Compaction, a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms.^[36]

Given sufficient time, an undifferentiated soil will evolve a soil profile which consists of two or more layers, referred to as soil horizons, that differ in one or more properties such as in their texture, structure, density, porosity, consistency, temperature, color, and reactivity.^[10] The horizons differ greatly in thickness and generally lack sharp boundaries; their development is dependent on the type of parent material, the processes that modify those parent materials, and the soil-forming factors that influence those processes. The biological influences on soil properties are strongest near the surface, while the geochemical influences on soil properties increase with depth. Mature soil profiles typically include three basic master horizons: A, B, and C. The solum normally includes the A and B horizons. The living component of the soil is largely confined to the solum, and is generally more prominent in the A horizon.^[37]

The soil texture is determined by the relative proportions of the individual particles of sand, silt, and clay that make up the soil. The interaction of the individual mineral particles with organic matter, water, gases via biotic and abiotic processes causes those particles to flocculate (stick together) to form aggregates or peds.^[38] Where these aggregates can be identified, a soil can be said to be developed, and can be described further in terms of color, porosity, consistency, reaction (acidity), etc. 

Water is a critical agent in soil development due to its involvement in the dissolution, precipitation, erosion, transport, and deposition of the materials of which a soil is composed.^[39] The mixture of water and dissolved or suspended materials that occupy the soil pore space is called the soil solution. Since soil water is never pure water, but contains hundreds of dissolved organic and mineral substances, it may be more accurately called the soil solution. Water is central to the dissolution, precipitation and leaching of minerals from the soil profile. Finally, water affects the type of vegetation that grows in a soil, which in turn affects the development of the soil, a complex feedback which is exemplified in the dynamics of banded vegetation patterns in semi-arid regions.^[40]

Soils supply plants with nutrients, most of which are held in place by particles of clay and organic matter (colloids)^[41] The nutrients may be adsorbed on clay mineral surfaces, bound within clay minerals (absorbed), or bound within organic compounds as part of the living organisms or dead soil organic matter. These bound nutrients interact with soil water to buffer the soil solution composition (attenuate changes in the soil solution) as soils wet up or dry out, as plants take up nutrients, as salts are leached, or as acids or alkalis are added.^[42][43]

Plant nutrient availability is affected by soil pH, which is a measure of the hydrogen ion activity in the soil solution. Soil pH is a function of many soil forming factors, and is generally lower (more acid) where weathering is more advanced.^[44]

Most plant nutrients, with the exception of nitrogen, originate from the minerals that make up the soil parent material. Some nitrogen originates from rain as dilute nitric acid and ammonia,^[45] but most of the nitrogen is available in soils as a result of nitrogen fixation by bacteria. Once in the soil-plant system, most nutrients are recycled through living organisms, plant and microbial residues (soil organic matter), mineral-bound forms, and the soil solution. Both living microorganisms and soil organic matter are of critical importance to this recycling, and thereby to soil formation and soil fertility.^[46] Microbial activity in soils may release nutrients from minerals or organic matter for use by plants and other microorganisms, sequester (incorporate) them into living cells, or cause their loss from the soil by volatilisation (loss to the atmosphere as gases) or leaching. 

History of studies[edit]

Fertility[edit]

The history of the study of soil is intimately tied to humans' urgent need to provide food for themselves and forage for their animals. Throughout history, civilizations have prospered or declined as a function of the availability and productivity of their soils.^[47]

The Greek historian Xenophon (450–355 BCE) is credited with being the first to expound upon the merits of green-manuring crops: "But then whatever weeds are upon the ground, being turned into earth, enrich the soil as much as dung."^[48]

Columella's "Husbandry," circa 60 CE, advocated the use of lime and that clover and alfalfa (green manure) should be turned under, and was used by 15 generations (450 years) under the Roman Empire until its collapse.^[48][49] From the fall of Rome to the French Revolution, knowledge of soil and agriculture was passed on from parent to child and as a result, crop yields were low. During the European Middle Ages, Yahya Ibn al-'Awwam's handbook,^[50] with its emphasis on irrigation, guided the people of North Africa, Spain and the Middle East; a translation of this work was finally carried to the southwest of the United States when under Spanish influence.^[51] Olivier de Serres, considered as the father of French agronomy, was the first to suggest the abandonment of fallowing and its replacement by hay meadows within crop rotations, and he highlighted the importance of soil (the French terroir) in the management of vineyards. His famous book Le Théâtre d’Agriculture et mesnage des champs^[52] contributed to the rise of modern, sustainable agriculture and to the collapse of old agricultural practices such as the lifting of forest litter for the amendment of crops (the French soutrage) and assarting, which ruined the soils of western Europe during Middle Ages and even later on according to regions.^[53]

Experiments into what made plants grow first led to the idea that the ash left behind when plant matter was burned was the essential element but overlooked the role of nitrogen, which is not left on the ground after combustion, a belief which prevailed until the 19th century.^[54] In about 1635, the Flemish chemist Jan Baptist van Helmont thought he had proved water to be the essential element from his famous five years' experiment with a willow tree grown with only the addition of rainwater. His conclusion came from the fact that the increase in the plant's weight had apparently been produced only by the addition of water, with no reduction in the soil's weight.^[55][56] John Woodward (d. 1728) experimented with various types of water ranging from clean to muddy and found muddy water the best, and so he concluded that earthy matter was the essential element. Others concluded it was humus in the soil that passed some essence to the growing plant. Still others held that the vital growth principal was something passed from dead plants or animals to the new plants. At the start of the 18th century, Jethro Tull demonstrated that it was beneficial to cultivate (stir) the soil, but his opinion that the stirring made the fine parts of soil available for plant absorption was erroneous.^[55][57]

As chemistry developed, it was applied to the investigation of soil fertility. The French chemist Antoine Lavoisier showed in about 1778 that plants and animals must [combust] oxygen internally to live and was able to deduce that most of the 165-pound weight of van Helmont's willow tree derived from air.^[58] It was the French agriculturalist Jean-Baptiste Boussingault who by means of experimentation obtained evidence showing that the main sources of carbon, hydrogen and oxygen for plants were air and water, while nitrogen was taken from soil.^[59] Justus von Liebig in his book Organic chemistry in its applications to agriculture and physiology (published 1840), asserted that the chemicals in plants must have come from the soil and air and that to maintain soil fertility, the used minerals must be replaced.^[60] Liebig nevertheless believed the nitrogen was supplied from the air. The enrichment of soil with guano by the Incas was rediscovered in 1802, by Alexander von Humboldt. This led to its mining and that of Chilean nitrate and to its application to soil in the United States and Europe after 1840.^[61]

The work of Liebig was a revolution for agriculture, and so other investigators started experimentation based on it. In England John Bennet Lawes and Joseph Henry Gilbert worked in the Rothamsted Experimental Station, founded by the former, and (re)discovered that plants took nitrogen from the soil, and that salts needed to be in an available state to be absorbed by plants. Their investigations also produced the "superphosphate", consisting in the acid treatment of phosphate rock.^[62] This led to the invention and use of salts of potassium (K) and nitrogen (N) as fertilizers. Ammonia generated by the production of coke was recovered and used as fertiliser.^[63] Finally, the chemical basis of nutrients delivered to the soil in manure was understood and in the mid-19th century chemical fertilisers were applied. However, the dynamic interaction of soil and its life forms still awaited discovery. 

In 1856 J. Thomas Way discovered that ammonia contained in fertilisers was transformed into nitrates,^[64] and twenty years later Robert Warington proved that this transformation was done by living organisms.^[65] In 1890 Sergei Winogradsky announced he had found the bacteria responsible for this transformation.^[66]

It was known that certain legumes could take up nitrogen from the air and fix it to the soil but it took the development of bacteriology towards the end of the 19th century to lead to an understanding of the role played in nitrogen fixation by bacteria. The symbiosis of bacteria and leguminous roots, and the fixation of nitrogen by the bacteria, were simultaneously discovered by the German agronomist Hermann Hellriegel and the Dutch microbiologist Martinus Beijerinck.^[62]

Crop rotation, mechanisation, chemical and natural fertilisers led to a doubling of wheat yields in western Europe between 1800 and 1900.^[67]

Formation[edit]

The scientists who studied the soil in connection with agricultural practices had considered it mainly as a static substrate. However, soil is the result of evolution from more ancient geological materials, under the action of biotic and abiotic (not associated with life) processes. After studies of the improvement of the soil commenced, others began to study soil genesis and as a result also soil types and classifications. 

In 1860, in Mississippi, Eugene W. Hilgard studied the relationship among rock material, climate, and vegetation, and the type of soils that were developed. He realised that the soils were dynamic, and considered soil types classification.^[68] Unfortunately his work was not continued. At about the same time, Friedrich Albert Fallou was describing soil profiles and relating soil characteristics to their formation as part of his professional work evaluating forest and farm land for the principality of Saxony. His 1857 book, Anfangsgründe der Bodenkunde (First principles of soil science) established modern soil science.^[69] Contemporary with Fallou's work, and driven by the same need to accurately assess land for equitable taxation, Vasily Dokuchaev led a team of soil scientists in Russia who conducted an extensive survey of soils, observing that similar basic rocks, climate and vegetation types lead to similar soil layering and types, and established the concepts for soil classifications. Due to language barriers, the work of this team was not communicated to western Europe until 1914 through a publication in German by Konstantin Dmitrievich Glinka, a member of the Russian team.^[70]

Curtis F. Marbut was influenced by the work of the Russian team, translated Glinka's publication into English,^[71] and as he was placed in charge of the U.S. National Cooperative Soil Survey, applied it to a national soil classification system.^[55]

Formation[edit]

Soil formation, or pedogenesis, is the combined effect of physical, chemical, biological and anthropogenic processes working on soil parent material. Soil is said to be formed when organic matter has accumulated and colloids are washed downward, leaving deposits of clay, humus, iron oxide, carbonate, and gypsum, producing a distinct layer called the B horizon. This is a somewhat arbitrary definition as mixtures of sand, silt, clay and humus will support biological and agricultural activity before that time. These constituents are moved from one level to another by water and animal activity. As a result, layers (horizons) form in the soil profile. The alteration and movement of materials within a soil causes the formation of distinctive soil horizons. However, more recent definitions of soil embrace soils without any organic matter, such as those regoliths that formed on Mars^[72] and analogous conditions in planet Earth deserts.^[73]

An example of the development of a soil would begin with the weathering of lava flow bedrock, which would produce the purely mineral-based parent material from which the soil texture forms. Soil development would proceed most rapidly from bare rock of recent flows in a warm climate, under heavy and frequent rainfall. Under such conditions, plants (in a first stage nitrogen-fixing lichens and cyanobacteria then epilithic higher plants) become established very quickly on basaltic lava, even though there is very little organic material. The plants are supported by the porous rock as it is filled with nutrient-bearing water that carries minerals dissolved from the rocks. Crevasses and pockets, local topography of the rocks, would hold fine materials and harbour plant roots. The developing plant roots are associated with mineral-weathering mycorrhizal fungi^[74] that assist in breaking up the porous lava, and by these means organic matter and a finer mineral soil accumulate with time. Such initial stages of soil development have been described on volcanoes,^[75] inselbergs,^[76] and glacial moraines.^[77]

Factors[edit]

How soil formation proceeds is influenced by at least five classic factors that are intertwined in the evolution of a soil. They are: parent material, climate, topography (relief), organisms, and time.^[78] When reordered to climate, relief, organisms, parent material, and time, they form the acronym CROPT.^[79]

Parent material[edit]

The mineral material from which a soil forms is called parent material. Rock, whether its origin is igneous, sedimentary, or metamorphic, is the source of all soil mineral materials and the origin of all plant nutrients with the exceptions of nitrogen, hydrogen and carbon. As the parent material is chemically and physically weathered, transported, deposited and precipitated, it is transformed into a soil. 

Typical soil parent mineral materials are:^[80]

Soil, on an agricultural field in Germany, which has formed on loess parent material.

Parent materials are classified according to how they came to be deposited. Residual materials are mineral materials that have weathered in place from primary bedrock. Transported materials are those that have been deposited by water, wind, ice or gravity. Cumulose material is organic matter that has grown and accumulates in place. 

Residual soils are soils that develop from their underlying parent rocks and have the same general chemistry as those rocks. The soils found on mesas, plateaux, and plains are residual soils. In the United States as little as three percent of the soils are residual.^[81]

Most soils derive from transported materials that have been moved many miles by wind, water, ice and gravity. 

Cumulose parent material is not moved but originates from deposited organic material. This includes peat and muck soils and results from preservation of plant residues by the low oxygen content of a high water table. While peat may form sterile soils, muck soils may be very fertile. 

Weathering[edit]

The weathering of parent material takes the form of physical weathering (disintegration), chemical weathering (decomposition) and chemical transformation. Generally, minerals that are formed under high temperatures and pressures at great depths within the Earth's mantle are less resistant to weathering, while minerals formed at low temperature and pressure environment of the surface are more resistant to weathering.^{[citation needed]} Weathering is usually confined to the top few meters of geologic material, because physical, chemical, and biological stresses and fluctuations generally decrease with depth.^[83] Physical disintegration begins as rocks that have solidified deep in the Earth are exposed to lower pressure near the surface and swell and become mechanically unstable. Chemical decomposition is a function of mineral solubility, the rate of which doubles with each 10 °C rise in temperature, but is strongly dependent on water to effect chemical changes. Rocks that will decompose in a few years in tropical climates will remain unaltered for millennia in deserts.^[7] Structural changes are the result of hydration, oxidation, and reduction. Chemical weathering mainly results from the excretion of organic acids and chelating compounds by bacteria^[84] and fungi,^[85] thought to increase under present-day greenhouse effect.^[86]

 

Sedimentary rocks are formed from eroded fragments of other rocks or even from the remains of plants or animals. The fragments accumulate in low-lying areas—lakes, oceans, and deserts—and then are compressed back into rock by the weight of overlying materials. Sandstone is formed from sand, mudstone from mud, and limestone from seashells, diatoms, or bonelike minerals precipitating out of calcium-rich water.

Fossils are most frequently found in sedimentary rock, which comes in layers, called strata.

Metamorphic rocks are sedimentary or igneous rocks that have been transformed by pressure, heat, or the intrusion of fluids. The heat may come from nearby magma or hot water intruding via hot springs. It can also come from subduction, when tectonic forces draw rocks deep beneath the Earth's surface.